Methods and systems for implantably monitoring external breathing therapy

ABSTRACT

An implantable device is used to monitor one or more conditions associated with an external breathing therapy delivered to the patient. The device may monitor therapy parameters including therapy effectiveness, impact of the therapy on the patient, therapy usage, compliance with a prescribed usage, therapy interactions, and/or other parameters.

RELATED APPLICATIONS

This application claims priority to provisional application U.S. Ser.No. 60/504,257, filed Sep. 18, 2003, and is a continuation of U.S.patent application Ser. No. 10/929,826, filed on Aug. 30, 2004, whichare hereby incorporated by reference in their respective entireties.

FIELD OF THE INVENTION

The present invention relates generally to therapy for sleep disorderedbreathing and, more particularly, to monitoring an external breathingtreatment delivered to a patient.

BACKGROUND OF THE INVENTION

The human body functions through a number of interdependentphysiological systems controlled through various mechanical, electrical,and chemical processes. The metabolic state of the body is constantlychanging. For example, as exercise level increases, the body consumesmore oxygen and gives off more carbon dioxide. The cardiac and pulmonarysystems maintain appropriate blood gas levels by making adjustments thatbring more oxygen into the system and dispel more carbon dioxide. Thecardiovascular system transports blood gases to and from the bodytissues. The respiration system, through the breathing mechanism,performs the function of exchanging these gases with the externalenvironment. Together, the cardiac and respiration systems form a largeranatomical and functional unit denoted the cardiopulmonary system.

Diseases and disorders of the pulmonary system affect a large group ofpatients. Obstructive pulmonary diseases may be associated with adecrease in the total volume of exhaled air flow caused by a narrowingor blockage of the airways. Examples of obstructive pulmonary diseasesinclude asthma, emphysema and bronchitis. Chronic obstructive pulmonarydisease (COPD) refers to chronic lung diseases that result in blockedair flow in the lungs. Chronic obstructive pulmonary disease generallydevelops over many years, typically from exposure to cigarette smoke,pollution, or other irritants. Over time, the elasticity of the lungtissue is lost, the lung's air sacs may collapse, the lungs may becomedistended, partially clogged with mucus, and lose the ability to expandand contract normally. As the disease progresses, breathing becomeslabored, and the patient grows progressively weaker. Many people withCOPD concurrently have both emphysema and chronic bronchitis.

Restrictive pulmonary diseases involve a decrease in the total volume ofair that the lungs are able to hold. Often the decrease in total lungvolume is due to a decrease in the elasticity of the lungs themselves,or may be caused by a limitation in the expansion of the chest wallduring inhalation. Restrictive pulmonary disease may be the result ofscarring from pneumonia, tuberculosis, or sarcoidosis. A decrease inlung volume may be caused by various neurologic and muscular diseasesaffecting the neural signals and/or muscular strength of the chest walland lungs. Examples of neurologic and/or muscular diseases that mayaffect lung volume include poliomyelitis and multiple sclerosis. Lungvolume deficiencies may also be related to congenital or acquireddeformities of the chest.

Pulmonary dysfunctions may also involve disorders of the pleural cavityand/or pulmonary vasculature. Pulmonary vasculature disorders mayinclude pulmonary hypertension, pulmonary edema, and pulmonary embolism.Disorders of the pleural cavity include conditions such as pleuraleffusion, pneumothorax, and hemothorax, for example.

Pulmonary diseases may be caused by infectious agents such as viraland/or bacterial agents. Examples of infectious pulmonary diseasesinclude pneumonia, tuberculosis, and bronchiectasis. Othernon-infectious pulmonary diseases include lung cancer and adultrespiratory distress syndrome (ARDS), for example.

Breathing disorders involving disrupted breathing rhythm, such as sleepapnea, hypopnea and periodic breathing, are respiratory systemconditions that affect a significant percentage of patients between 30and 60 years. Disordered breathing may be caused, for example, by anobstructed airway, or by derangement of the signals from the braincontrolling respiration. Sleep disordered breathing is associated withexcessive daytime sleepiness, systemic hypertension, increased risk ofstroke, angina and myocardial infarction. Disordered breathing isrelated to congestive heart failure and can be particularly serious forpatients concurrently suffering from cardiovascular deficiencies.

Various types of disordered breathing have been identified, including,apnea (interrupted breathing), hypopnea (shallow breathing), tachypnea(rapid breathing), hyperpnea (heavy breathing), and dyspnea (laboredbreathing). Combinations of the respiratory cycles described above maybe observed, including, for example, periodic breathing andCheyne-Stokes respiration (CSR). Cheyne-Stokes respiration isparticularly prevalent among heart failure patients, and may contributeto the progression of heart failure.

Pulmonary diseases and disorders including those described herein havebeen treated using a variety of patient-external breathing therapydevices. Monitoring parameters associated with external breathingtherapy provides an opportunity to provide feedback for enhanced therapydelivery. Effective approaches to monitoring and/or adjusting externalbreathing therapy are needed. The present invention fulfills these andother needs, and addresses other deficiencies of prior artimplementations and techniques.

SUMMARY OF THE INVENTION

Embodiments of the invention are directed to methods and systems formonitoring therapy delivered to a patient. An embodiment of theinvention involves a method for implantably monitoring apatient-external respiration therapy delivered to the patient. Themethod includes sensing one or more conditions associated withpatient-external breathing therapy. The patient-external respirationtherapy is monitored by an implantable device based on the sensedconditions.

In accordance with another embodiment of the invention, a medicalsystem, includes a sensing system configured to sense conditionsassociated with a patient-external breathing therapy. The system alsoincludes an implantable monitoring device, coupled to the sensingsystem. The implantable monitoring device is configured to monitor thepatient-external breathing therapy based on the one or more sensedconditions.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are flowcharts illustrating methods of implantablymonitoring an externally delivered breathing therapy in accordance withembodiments of the invention;

FIG. 1F is a graph of respiratory pressure with respect to timeillustrating a respiratory pressure notch observable when a patient isusing a breathing therapy device;

FIG. 2 is a block diagram of a medical system that may be used toprovide patient monitoring and external breathing therapy in accordancewith embodiments of the invention;

FIG. 3 illustrates a medical system including an implantable cardiacrhythm management device that may be used to monitor parameters of abreathing therapy delivered by a patient-external respiration therapydevice in accordance with an embodiment of the invention;

FIG. 4A is a partial view of an implantable medical device that may beused for coordinated patient monitoring, diagnosis, and/or therapy inaccordance with an embodiment of the invention;

FIG. 4B is a partial view of an implantable subcutaneous medical devicethat may be used for coordinated patient monitoring, diagnosis, and/ortherapy in accordance with an embodiment of the invention;

FIG. 5 is a block diagram of an implantable cardiac rhythm managementsystem that may be used to monitor external breathing therapy inaccordance with embodiments of the invention;

FIG. 6 is a block diagram of a patient-external respiratory therapydevice that may be used to provide breathing therapy monitored by animplantable device in accordance with embodiments of the invention;

FIG. 7 is a graph of a respiration signal measured by a transthoracicimpedance sensor that may be utilized for monitoring parameters of abreathing therapy in accordance with embodiments of the invention;

FIG. 8 is a block diagram of a sleep detector in accordance withembodiments of the invention;

FIG. 9 is a flow chart illustrating a sleep detection method based onsignals from an accelerometer and a minute ventilation sensor inaccordance with embodiments of the invention;

FIG. 10A is a graph of an accelerometer signal indicating patientactivity level that may be used for sleep detection in accordance withembodiments of the invention;

FIG. 10B is a graph of a patient's heart rate and sensor indicated ratethat may be used for sleep detection in accordance with an embodiment ofthe invention;

FIG. 11 is a graph of baseline trending for an MV signal used for sleepdetection in accordance with embodiments of the invention;

FIG. 12 illustrates adjustment of an accelerometer sleep threshold usingan MV signal in accordance with embodiments of the invention

FIG. 13 is a respiration signal graph illustrating respiration intervalsused for disordered breathing detection according to embodiments of theinvention;

FIG. 14 is a graph of a respiration signal illustrating variousintervals that may be used for detection of apnea in accordance withembodiments of the invention;

FIGS. 15A and 15B are respiration graphs illustrating normal respirationand abnormally shallow respiration utilized in detection of disorderedbreathing in accordance with embodiments of the invention;

FIG. 16 is a flow chart illustrating a method of apnea and/or hypopneadetection according to embodiments of the invention;

FIG. 17 is a respiration graph illustrating a breath interval utilizedin connection with disordered breathing detection in accordance withembodiments of the invention;

FIG. 18 is a respiration graph illustrating a hypopnea detectionapproach in accordance with embodiments of the invention;

FIGS. 19 and 20 provide charts illustrating classification of individualdisordered breathing events and series of periodically recurringdisordered breathing events, respectively, in accordance withembodiments of the invention;

FIGS. 21A-E are graphs illustrating respiration patterns that may bedetected as disordered breathing episodes in accordance with embodimentsof the invention;

FIG. 22 is a flow graph of a method for detecting disordered breathingin accordance with embodiments of the invention; and

FIGS. 23 and 24 are flow charts illustrating methods of adapting adisordered breathing therapy according to embodiments of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings which form a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

Breathing disorders may be more effectively monitored and/or treatedusing a coordinated approach. Various embodiments of the invention areimplemented using medical systems employing two or more patient-externaland/or patient-internal medical devices. The medical devices maycommunicate or otherwise operate in concert to provide morecomprehensive patient monitoring for external breathing therapy.

A number of disorders are treated using external breathing therapydevices. For example, rhythm related breathing disorders such as sleepapnea, hypopnea may be treated with a positive airway pressure device.Asthma may be treated with a nebulizer. Various diseases affecting thepulmonary system may be treated with gas or oxygen therapy. Embodimentsof the invention are directed to methods and systems utilizing animplantable device to monitor parameters associated with an externalbreathing therapy delivered to the patient. External breathing therapymay be delivered by various types of patient-external respiratorytherapy devices, including, for example, nebulizers, respirators,ventilators, external gas therapy devices and/or positive airwaypressure devices.

A typical continuous positive airway pressure (CPAP) device delivers airpressure through a nasal mask worn by the patient. The application ofcontinuous positive airway pressure keeps the patient's throat open,reducing or eliminating the obstruction causing apnea. Positive airwaypressure devices may be used to provide a variety of respirationtherapies, including, for example, continuous positive airway pressure(CPAP), bi-level positive airway pressure (bi-level PAP), proportionalpositive airway pressure (PPAP), auto-titrating positive airwaypressure, ventilation, gas or oxygen therapies. Some positive airwaypressure devices may also be configured to provide both positive andnegative pressure, such that negative pressure is selectively used (andde-activated) when necessary, such as when treating Cheyne-Stokesbreathing, for example. The term xPAP will be used herein as a genericterm for any device using forms of positive airway pressure (andnegative pressure when necessary), whether continuous or otherwise.

The parameters monitored by the monitoring system may include therapyeffectiveness, impact of the therapy on the patient, therapy usage,compliance with a prescribed usage and/or therapy interactions, forexample. In various embodiments described herein, sensors coupled to theimplantable monitoring device sense conditions used to monitor therapyparameters. For example, the sensed conditions may be used to evaluatethe effectiveness of the breathing therapy the impact of the therapy onthe patient and/or therapy interactions between the external breathingtherapy and other therapies delivered to the patient. The externalbreathing therapy may be adjusted to enhance therapy effectiveness, toreduce an impact of the therapy and/or to reduce therapy interactions.The implantable device may monitor the patient's use of the externalbreathing therapy and/or compliance with a prescribed usage of thebreathing therapy, for example.

The implantable device may transmit information about the sensedconditions and/or the monitored parameters to the external breathingtherapy device. The information may be used by the external breathingtherapy device to automatically adjust the breathing therapy deliveredto the patient. The information may be transmitted, either by theimplantable device, or by the external breathing therapy device, to apatient management system. Advanced patient management (APM) systemsinvolve a system of medical devices that are accessible through variouscommunications technologies. Medical information may be transmitted to aremote patient management server from the various medical devices. Themedical information may be analyzed and used to diagnose and/or monitordisease progression, to determine appropriate therapies for the patient,and/or for other medical purposes.

Information acquired by the monitoring device, including informationassociated with the sensed conditions and/or the parameters of thebreathing therapy, may be evaluated to facilitate diagnosis and/ortherapy adjustment. The information transmitted to the patientmanagement system may be used for diagnostic purposes related to thebreathing disorder affecting the patient, for example. The patientmanagement system may adjust breathing therapy delivery based on theinformation. In one implementation, the patient management systemtransmits control signals to the breathing therapy device to adjust thebreathing therapy. Further, the patient and/or the patient's physicianmay access the information through the patient management system.

FIGS. 1A-E are flowcharts illustrating methods related to implantablymonitoring external breathing therapy in accordance with variousembodiments of the invention. As illustrated in the flowchart of FIG.1A, a method for monitoring external breathing treatment involvessensing 102 one or more conditions associated with patient-externalbreathing therapy and implantably monitoring 104 the patient-externalbreathing therapy based on the one or more sensed conditions. The sensedconditions are used to monitor one or more parameters of thepatient-external breathing therapy, such as the patient's compliancewith the external breathing therapy, the effectiveness of the externalbreathing therapy, the impact of the external breathing therapy on thepatient, and/or other conditions. The parameters monitored by theimplantable device, and the conditions sensed to monitor the breathingtherapy parameters can be programmable. The implantable device mayacquire information used to monitor the breathing therapy parameterscontinuously or during selected periods of time. For example, if thepatient suffers from sleep disordered breathing, the implantable devicemay acquire information associated with the breathing therapy afterdetecting that the patient is asleep. Information acquired by theimplantable device based on the sensed conditions may be stored,displayed, printed, trended and/or transmitted from the implantabledevice to another device, such as a patient-external device, implantabledevice, therapy device, device programmer, and/or advanced patientmanagement server. Information associated with the monitored parameters,e.g., therapy usage, may be stored, displayed, printed, trended, and/ortransmitted from the implantable device to another device

FIG. 1B is a flowchart illustrating a method for monitoring theeffectiveness of an externally delivered breathing therapy using animplantable device. The patient's respiration is sensed 106 and arespiration waveform is generated 108. The sensed respiration waveformis used by the implantable device to detect 110 disordered breathingevents. An apnea/hypopnea index (AHI) is calculated 112 based on thedetected disordered breathing events. The AHI is used to assess theeffectiveness 114 of the breathing treatment. A lower AHI may indicate amore effective breathing treatment than a relatively higher AHI, forexample. The therapy effectiveness information may be transmitted 116 tothe external breathing therapy device and/or to an APM server. Thetherapy effectiveness data may be used 118 by the external breathingtherapy device, or by the APM device, for example, to adjust theexternal breathing therapy. The therapy adjustment may be performedautomatically by the APM or by the external breathing therapy device.The therapy adjustment may be performed manually by the patient'sphysician based on the effectiveness information.

External breathing therapy may be inconvenient to use and uncomfortableto the patient. As a result, the patient may limit the use of thetherapy. For example, if the use of the breathing therapy interfereswith the patient's ability to sleep, the patient may stop using thebreathing therapy, or may use the breathing therapy infrequently. Thepatient may not keep track of how frequently he or she uses thebreathing therapy and may not be able to accurately report breathingtherapy compliance to the physician.

FIG. 1C is a flowchart of a method for implantably monitoring apatient's usage of the external breathing therapy. In this example,usage of an external breathing therapy for sleep disordered breathing isdetermined based on the patient's proximity to the external breathingtherapy device during sleep. As illustrated in FIG. 1C, one or moreconditions indicative of sleep may be sensed 122. The implantable devicedetects 124 sleep based on the sensed sleep-related conditions. Theproximity of the patient to the external breathing therapy device issensed 126.

The proximity of the patient to the external breathing therapy devicemay be determined using a transmitter coupled to the external breathingtherapy device and a receiver in the implantable monitoring device. Ifthe patient is near the external breathing therapy device, the receiverreceives a signal broadcast by the transmitter. The transmitter may belocated on a bedside unit of the external breathing therapy device, oron the respiratory mask of the external breathing therapy device, forexample.

The implantable device monitors 128 the patient's usage of externalbreathing therapy based on the proximity of the patient to the externalbreathing therapy device during sleep. Other methods of determiningpatient usage of the external breathing therapy device may also beimplemented. For example, the morphology of the patient's respirationwaveform during external breathing therapy may be detectably differentfrom the patient's respiration waveform when therapy is not beingdelivered. The implantable device may sense the patient's respirationand monitor usage of the external breathing therapy device based onevaluation of the patient's respiration waveform.

The implantable device may monitor patient compliance with respect to aprescribed breathing therapy. The implantable device may transmitinformation related to the patient compliance to an external device,such as a patient management device accessible to the patient and/or thepatient's physician. The information may be used to alert to the patientand/or to the patient's physician when the patient's compliance with theprescribed breathing therapy drops below a threshold level.

FIG. 1D is a flowchart of a method for implantably monitoring patientcompliance with a prescribed breathing therapy in accordance withembodiments of the invention. Breathing therapy is delivered to thepatient using a patient external device. The patient's use of externallydelivered breathing therapy is monitored 140 using an implantabledevice.

In one implementation, the implantable device may monitor patient use ofthe breathing therapy may by sensing the proximity of the patient to thebreathing therapy unit. According to this approach, if the patient iswithin a selected proximity range of the patient-external breathingtherapy unit, then the patient is assumed to be using the breathingtherapy.

Another approach to monitoring patient compliance with breathing therapyinvolves analyzing the respiratory waveform of the patient. For example,the implantable device may sense the transthoracic impedance of thepatient to determine the patient's respiratory waveform. The patient'suse of the breathing therapy may be determined by detecting features ofthe respiratory waveform indicative of breathing therapy usage. In onescenario, use of the breathing therapy may be determined by comparingthe morphology of a patient's respiratory waveform during therapy to themorphology of the patient's respiratory waveform without therapy. Thepatient's respiratory waveforms with and without therapy may be comparedto detect features that indicate usage. For example, the patient may bedetermined to be using the breathing therapy if the patient'srespiratory waveform exhibits a pressure notch indicative of flowcontrolled breathing therapy usage. FIG. 1F illustrates a graph ofrespiratory pressure 198 with respect to time. The notch 199 on thepressure graph indicates that the patient is using the breathing therapydevice.

In another example, patient compliance with the prescribed breathingtherapy may be determined based on night to night changes in therapyeffectiveness. For example, if the therapy effectiveness stays constantor changes slowly over the course of several nights, it may bedetermined that the patient is using the breathing therapy asprescribed. Usage of the therapy may be determined by using a baselineof therapy effectiveness developed over several nights. If the therapyeffectiveness drops significantly from the baseline, then the patientmay have stopped using the therapy device.

Returning to FIG. 1D, information related to the patient's use of thebreathing therapy may be collected and/or evaluated by the implantabledevice, including, for example, the times the patient used the breathingtherapy, the duration of the usage, the frequency of usage, and/or otherinformation. The patient's compliance with a prescribed breathingtherapy may be determined 142 by comparing the actual use to theprescribed use. In one scenario, the compliance determination may beperformed by the implantable device. In another scenario, informationrelated to the patient use of the breathing therapy may be transmitted144 to a remote device, such as the breathing therapy device or apatient management device, where the analysis is performed. The patientand/or the patient's physician may be alerted 150 to the patient'scompliance with the breathing therapy. In one scenario, the patientand/or the patient's physician may be alerted if the patient'scompliance decreases below a threshold value. The patient may bereminded to use the breathing therapy. If patient compliance is low, thephysician and/or the patient may adjust the therapy to increasebreathing therapy compliance.

In accordance with one embodiment, the breathing therapy may beimplantably monitored for therapy effectiveness and impact to thepatient. The flowchart of FIG. 1E illustrates an example methodinvolving the use of a monitoring device configured as a component of animplantable cardiac device to monitor breathing therapy delivered by acontinuous positive airway pressure (CPAP) device. In this example,therapy for sleep disordered breathing is delivered to the patient usinga continuous positive airway pressure (CPAP) device. The effectivenessof the breathing therapy and the impact of the therapy on the patientare monitored by an implantable cardiac device.

Sensors coupled to the implantable monitoring device sense one or morepatient conditions related to therapy effectiveness. For example, therespiration of the patient may be sensed 152 and the monitoring devicemay detect 154 disordered breathing episodes based on the respirationsignal. The monitoring device may monitor therapy effectiveness bymonitoring the severity, frequency and/or duration of sleep disorderedbreathing episodes experienced by the patient. In one implementation,the monitoring device may calculate 156 an apnea/hypopnea index (AHI)and/or a percent time in periodic breathing (% PB) indicative of thefrequency of disordered breathing episodes. The effectiveness of theCPAP therapy may be monitored 160 based on the calculated indices. Ifthe AHI and/or % PB are relatively low, the breathing therapy may bedetermined to be effective.

A CPAP device typically includes a respiratory mask, e.g., a nasal orfacial mask, worn by the patient to facilitate delivery of air or othergas to the patient's airway. The respiratory mask may be inconvenientand/or uncomfortable for the patient to wear and may keep the patientawake. Further, delivery of positive airway pressure may disturb thepatient, inhibit sleep, and/or cause the patient to arouse frequently.Sleep disturbances may be more frequent and/or severe if the CPAPtherapy pressure is too high. Information about these side effects ofthe breathing therapy may be helpful in tailoring a therapy regimen forthe patient. The monitoring device may monitor the impact of the CPAPtherapy on the patient based on one or more sensed conditions indicativeof the impact of the therapy on the patient.

In one example, the one or more sensed conditions 162 relate to sleepand may be used to detect 164 sleep and/or arousals from sleep. Themonitoring unit implemented in an implantable cardiac device may monitor166 the impact of the CPAP therapy on the patient by monitoring thepatient's sleep. For example, the monitoring unit may monitor the totaltime the patient spends sleeping, the number of arousals experienced bythe patient in one night, and/or the depth of the arousals. In oneimplementation the cardiac device may calculate the number of arousalsexperienced by the patient per hour (A/h).

The therapy effectiveness and impact information may be transmitted 168to the CPAP device and/or an APM server. The information may be used toautomatically or manually adjust the therapy delivered to the patient.For example, if the AHI is high, the breathing therapy pressure may beadjusted upward to provide a more effective therapy. If the patientexperiences an arousal rate, e.g., A/h, greater than a threshold withoutexperiencing sleep disordered breathing episodes, the therapy may bedetermined to be too aggressive. The breathing therapy pressure may beadjusted downward to provide a disordered breathing therapy that is morecomfortable to the patient and allows the patient to sleep with fewerinterruptions.

FIG. 2 is a block diagram of a medical system 200 that may be used toimplement coordinated patient monitoring and therapy in accordance withembodiments of the invention. The medical system 200 may include, forexample, a patient-internal monitoring device 210 and a patient-externalbreathing therapy device 220.

The patient-internal monitoring device 210 may be a fully or partiallyimplantable device that monitors breathing therapy delivered to thepatient by the therapy device 220. The patient-external breathingtherapy device 220 is external to the patient (i.e., not invasivelyimplanted within the patient's body). The patient-external therapydevice 220 may be positioned on the patient, near the patient, or in anylocation external to the patient. It is understood that a portion of apatient-external therapy device 220 may be positioned within an orificeof the body, such as the nasal cavity or mouth, yet can be consideredexternal to the patient (e.g., mouth pieces/appliances, tubes/appliancesfor nostrils, or temperature sensors positioned in the ear canal).

The patient-internal device 210 may be coupled to one or more sensors241, 242, patient input devices 243 and/or other information acquisitiondevices 244. The sensors 241, 242, patient input devices 243, and/orother information acquisition devices 244 may be employed to detectconditions relevant to the breathing therapy delivered by thepatient-external therapy device 220. The patient-external device 220 mayalso be coupled to one or more sensors 246 and/or other informationdevices. Information from the sensors 246, e.g., flow sensors, pressuresensors, and/or other input devices, e.g., patient input devices and/ornetwork based information servers coupled to the patient-external device220 may be used by the therapy device 220 to adjust the therapydelivered by the patient external device 220. In some implementations,sensed or detected information acquired by the patient external device220 may be transmitted from the patient-external device 220 to thepatient-internal device 210. The transmitted information may be used inconnection with the monitoring functions of the patient internal device210.

In one implementation, the patient-internal device 210 is coupled to oneor more patient-internal sensors 241 that are fully or partiallyimplantable within the patient. The patient-internal device 210 may alsobe coupled to patient-external sensors 242 positioned on, near, or in aremote location with respect to the patient. The patient-internal 241and patient-external 242 sensors may be used to sense variousparameters, such as physiological or environmental parameters related tothe breathing therapy delivered by the patient-external therapy device.

The patient-internal sensors 241 may be coupled to the patient-internalmedical device 210 through internal leads. For example, an internalendocardial lead system may be used to couple cardiac electrodes forsensing cardiac electrical activity to an implantable pacemaker or othercardiac device that includes a monitoring unit as described herein.Alternatively one or more patient-internal sensors 241 may be equippedwith transceiver circuitry to support wireless communication between theone or more patient-internal sensors 241 and the patient-internalmedical device 210. Patient-external sensors 242 are preferablywirelessly coupled to the patient-internal device 210.

The patient-internal device 210 may be coupled to one or morepatient-input devices 243. The patient-input devices 243 allow themanual transfer of information to the patient-internal device 210. Thepatient-input devices 243 may be particularly useful for allowing thepatient to input information concerning patient perceptions, such as howwell the patient feels, and information such as patient smoking, druguse, or other activities that are not automatically sensed or detectedby the medical devices 210.

The patient-internal device 210 may be connected to one or moreinformation systems 244, for example, a database or information serverthat provides information useful in connection with the monitoringfunctions of the patient-internal device 210. For example, thepatient-internal device 210 may be coupled through a network such as theinternet to a information system server that provides information aboutenvironmental conditions affecting the patient, e.g., the pollutionindex for the patient's location. Internal sensors, external sensors,patient input devices and/or information systems similar to thosedescribed above may also be coupled to the patient-external therapydevice.

In one embodiment, the patient-internal device 210 and thepatient-external therapy device 220 may communicate through a wirelesslink between the devices 210, 220. For example, the patient-internal andpatient-external devices 210, 220 may be coupled through a short-rangeradio link, such as Bluetooth or a proprietary wireless link. Thecommunications link may facilitate uni-directional or bi-directionalcommunication between the patient-internal 210 and patient-external 220medical devices. Data and/or control signals may be transmitted betweenthe patient-internal 210 and patient-external 220 medical devices tocoordinate or control the functions of the medical devices 210, 220.

In another embodiment of the invention, the patient-internal andpatient-external medical devices 210, 220 may be used within thestructure of an advanced patient management system. Advanced patientmanagement systems involve a system of medical devices that areaccessible through various communications technologies. For example,patient data may be downloaded from one or more of the medical devicesin the system periodically or on command, and stored at a patientinformation server. The physician and/or the patient may communicatewith the medical devices and the patient information server, forexample, to acquire patient data or to initiate, terminate or modifytherapy.

In the implementation illustrated in FIG. 2, the patient-internalmedical device 210 and the patient-external medical device 220 may becoupled through wireless or wired communication links to a patientinformation server that is part of an advanced patient management (APM)system 230. The APM patient information server 230 may be used todownload and store data collected by the patient-internal andpatient-external medical devices 210, 220. In one implementation, thepatient internal device 210 and/or the patient-external device 220 maybe communicatively coupled to device programmers 260, 270. Theprogrammer 260 may provide indirect communication between the patientinternal device 210 and the patient information server 230. Theprogrammer 270 may provide indirect communication between the patientexternal device 220 and the patient information server 230.

The data stored on the APM patient information server 230 may beaccessible by the patient and/or the patient's physician throughterminals 250, e.g., remote computers located in the patient's home orthe physician's office. The APM patient information server 230 may becommunicate with one or more of the patient-internal andpatient-external medical devices 210, 220 to effect remote control ofthe monitoring, diagnosis, and/or therapy functions of the medicaldevices 210, 220.

In one scenario, the patient's physician may access patient datatransmitted from the monitoring device 210 to the APM patientinformation server 230. After evaluation of the collected information,the patient's physician may communicate with the patient-externaltherapy device 220 through the APM system 230 to initiate, terminate, ormodify the therapy functions of the patient-external therapy device 220.Systems and methods involving advanced patient management techniques arefurther described in U.S. Pat. Nos. 6,336,903, 6,312,378, 6,270,457, and6,398,728 which are incorporated herein by reference.

In one implementation, the patient-internal and patient-external medicaldevices 210, 220 may not communicate directly, but may communicateindirectly through the APM system 230. In this embodiment, the APMsystem 230 may operate as an intermediary between two or more of themedical devices 210, 220. For example, information collected by thepatient-internal medical device 210 may be transferred from thepatient-internal medical device 210 to the APM system 230. The APMsystem 230 may transfer the collected information to thepatient-external therapy device 220.

FIG. 3 illustrates a block diagram of medical system 300 that may beused to implantably monitor breathing therapy delivered by apatient-external device in accordance with an embodiment of theinvention. In this example, the medical system 300 includes animplantable cardiac rhythm management (CRM) device 310 incorporating amonitoring unit 311 that monitors one or more parameters of breathingtherapy delivered by a breathing therapy device 320. In thisconfiguration, the monitoring unit 311 within the implantable cardiacrhythm management device (CRM) 310 operates as the patient-internalmedical device described in connection with FIG. 2. The CRM 310incorporating the monitoring unit 311 may provide additional monitoring,diagnostic, and/or therapeutic functions to the patient.

The CRM 310 may be electrically coupled to the patient's heart throughelectrodes placed in, on, or about the heart. The cardiac electrodes maysense cardiac signals produced by the heart and/or provide therapy toone or more heart chambers. For example, the cardiac electrodes maydeliver electrical stimulation to one or more heart chambers, and/or toone or multiple sites within the heart chambers. The CRM 310 maydirectly control delivery of one or more cardiac therapies, such ascardiac pacing, defibrillation, cardioversion, cardiacresynchronization, and/or other cardiac therapies, for example.

In the example illustrated in FIG. 3, the breathing therapy device 320comprises a positive airway pressure device. Other types of externalbreathing therapy may be monitored by the monitoring unit 311, such asbreathing treatment delivered by a nebulizer, respirator, ventilator orgas therapy device.

In the configuration illustrated in FIG. 3, the xPAP device 320 operatesas a patient-external therapy device, as discussed in connection withFIG. 2. The xPAP device 320 develops a positive air pressure that isdelivered to the patient's airway through tubing 352 and mask 354connected to the xPAP device 320. Positive airway pressure devices areoften used to treat disordered breathing, including central and/orobstructive disordered breathing types. In one configuration, forexample, the positive airway pressure provided by the xPAP device 320acts as a pneumatic splint keeping the patient's airway open andreducing the severity and/or number of occurrences of disorderedbreathing due to airway obstruction.

The monitoring unit 311 may monitor one or more parameters associatedwith the breathing therapy delivered by the xPAP device 320. The CRM 310may communicate the information related to the breathing treatment tothe xPAP device 320 through a wireless communications link, for example.Alternatively, or additionally, the CRM 310 and xPAP 320 devices maycommunicate with and/or through an APM system 330, as described above.

FIG. 4A is a partial view of an implantable device that may includecircuitry for monitoring external breathing therapy 435 in accordancewith embodiments of the invention. In this example, the implantabledevice comprises a cardiac rhythm management device (CRM) 400 includingan implantable pulse generator 405 electrically and physically coupledto an intracardiac lead system 410. The external breathing therapymonitoring system may alternatively be implemented in a variety ofimplantable monitoring, diagnostic, and/or therapeutic devices, such asan implantable cardiac monitoring device, an implantable drug deliverydevice, or an implantable neurostimulation device, for example.

Portions of the intracardiac lead system 410 are inserted into thepatient's heart 490. The intracardiac lead system 410 includes one ormore electrodes configured to sense electrical cardiac activity of theheart, deliver electrical stimulation to the heart, sense the patient'stransthoracic impedance, and/or sense other physiological parameters,e.g., cardiac chamber pressure or temperature. Portions of the housing401 of the pulse generator 405 may optionally serve as a can electrode.

Communications circuitry is disposed within the housing 401 forfacilitating communication between the pulse generator 405 and anexternal device, such as the external breathing therapy device or APMsystem. The communications circuitry can also facilitate unidirectionalor bidirectional communication with one or more implanted, external,cutaneous, or subcutaneous physiologic or non-physiologic sensors,patient-input devices and/or information systems.

The pulse generator 405 may optionally incorporate a motion sensor 420.The motion sensor 420 may be configured to sense patient activity.Patient activity may be used in connection with sleep detection asdescribed in more detail herein. The motion sensor 420 may beimplemented as an accelerometer positioned in or on the housing 401 ofthe pulse generator 405. If the motion sensor is implemented as anaccelerometer, the motion sensor may also provide acoustic information,e.g. rales, coughing, and cardiac, e.g. S1-S4 heart sounds, murmurs, andother acoustic information.

The lead system 410 of the CRM 400 may incorporate a transthoracicimpedance sensor that may be used to acquire the patient's respirationwaveform, or other respiration-related information. The transthoracicimpedance sensor may include, for example, one or more intracardiacelectrodes 441, 442, 451-455, 463 positioned in one or more chambers ofthe heart 490. The intracardiac electrodes 441, 442, 451-455, 463 may becoupled to impedance drive/sense circuitry 430 positioned within thehousing of the pulse generator 405.

In one implementation, impedance drive/sense circuitry 430 generates acurrent that flows through the tissue between an impedance driveelectrode 451 and a can electrode on the housing 401 of the pulsegenerator 405. The voltage at an impedance sense electrode 452 relativeto the can electrode changes as the patient's transthoracic impedancechanges. The voltage signal developed between the impedance senseelectrode 452 and the can electrode is detected by the impedance sensecircuitry 430. Other locations and/or combinations of impedance senseand drive electrodes are also possible.

The voltage signal developed at the impedance sense electrode 452,illustrated in FIG. 7, is proportional to the patient's transthoracicimpedance and represents the patient's respiration waveform. Thetransthoracic impedance increases during respiratory inspiration anddecreases during respiratory expiration. The peak-to-peak transition ofthe transthoracic impedance is proportional to the amount of air movedin one breath, denoted the tidal volume. The amount of air moved perminute is denoted the minute ventilation. A normal “at rest” respirationpattern, e.g., during non-REM sleep, includes regular, rhythmicinspiration—expiration cycles without substantial interruptions, asindicated in FIG. 7.

Returning to FIG. 4A, the lead system 410 may include one or morecardiac pace/sense electrodes 451-455 positioned in, on, or about one ormore heart chambers for sensing electrical signals from the patient'sheart 490 and/or delivering pacing pulses to the heart 490. Theintracardiac sense/pace electrodes 451-455, such as those illustrated inFIG. 4A, may be used to sense and/or pace one or more chambers of theheart, including the left ventricle, the right ventricle, the leftatrium and/or the right atrium. The lead system 410 may include one ormore defibrillation electrodes 441, 442 for deliveringdefibrillation/cardioversion shocks to the heart.

The pulse generator 405 may include circuitry for detecting cardiacarrhythmias and/or for controlling pacing or defibrillation therapy inthe form of electrical stimulation pulses or shocks delivered to theheart through the lead system 410. Circuitry for monitoring externalbreathing therapy 435, including sensor interface circuitry, eventdetectors, monitoring processor, and/or memory circuitry, as describedin connection with the FIG. 6, may be housed within the pulse generator405. The monitoring circuitry may be coupled to various sensors, patientinput devices, and/or information systems through leads or throughwireless communication links.

FIG. 4B is a diagram illustrating an implantable transthoracic cardiacdevice that may be used in connection with developing feedbackinformation for sleep disordered breathing therapy in accordance withembodiments of the invention. The implantable device illustrated in FIG.4B is an implantable transthoracic cardiac sensing and/or stimulation(ITCS) device that may be implanted under the skin in the chest regionof a patient. The ITCS device may, for example, be implantedsubcutaneously such that all or selected elements of the device arepositioned on the patient's front, back, side, or other body locationssuitable for sensing cardiac activity and delivering cardiac stimulationtherapy. It is understood that elements of the ITCS device may belocated at several different body locations, such as in the chest,abdominal, or subclavian region with electrode elements respectivelypositioned at different regions near, around, in, or on the heart.

Circuitry for implementing a monitoring device or monitoring device anda therapy feedback unit may be positioned within the primary housing ofthe ITCS device. The primary housing (e.g., the active or non-activecan) of the ITCS device, for example, may be configured for positioningoutside of the rib cage at an intercostal or subcostal location, withinthe abdomen, or in the upper chest region (e.g., subclavian location,such as above the third rib). In one implementation, one or moreelectrodes may be located on the primary housing and/or at otherlocations about, but not in direct contact with the heart, great vesselor coronary vasculature.

In another implementation, one or more electrodes may be located indirect contact with the heart, great vessel or coronary vasculature,such as via one or more leads implanted by use of conventionaltransveous delivery approaches. In another implementation, for example,one or more subcutaneous electrode subsystems or electrode arrays may beused to sense cardiac activity and deliver cardiac stimulation energy inan ITCS device configuration employing an active can or a configurationemploying a non-active can. Electrodes may be situated at anteriorand/or posterior locations relative to the heart.

In the configuration shown in FIG. 4B, a subcutaneous electrode assembly407 can be positioned under the skin in the chest region and situateddistal from the housing 402. The subcutaneous and, if applicable,housing electrode(s) can be positioned about the heart at variouslocations and orientations, such as at various anterior and/or posteriorlocations relative to the heart. The subcutaneous electrode assembly 407is coupled to circuitry within the housing 402 via a lead assembly 406.One or more conductors (e.g., coils or cables) are provided within thelead assembly 406 and electrically couple the subcutaneous electrodeassembly 407 with circuitry in the housing 402. One or more sense,sense/pace or defibrillation electrodes can be situated on the elongatedstructure of the electrode support, the housing 402, and/or the distalelectrode assembly (shown as subcutaneous electrode assembly 407 in FIG.4B).

It is noted that the electrode and the lead assemblies 407, 406 can beconfigured to assume a variety of shapes. For example, the lead assembly406 can have a wedge, chevron, flattened oval, or a ribbon shape, andthe subcutaneous electrode assembly 407 can comprise a number of spacedelectrodes, such as an array or band of electrodes. Moreover, two ormore subcutaneous electrode assemblies 407 can be mounted to multipleelectrode support assemblies 406 to achieve a desired spacedrelationship amongst subcutaneous electrode assemblies 407.

In particular configurations, the ITCS device may perform functionstraditionally performed by cardiac rhythm management devices, such asproviding various cardiac monitoring, pacing and/orcardioversion/defibrillation functions. Exemplary pacemaker circuitry,structures and functionality, aspects of which can be incorporated in anITCS device of a type that may benefit from multi-parameter sensingconfigurations, are disclosed in commonly owned U.S. Pat. Nos.4,562,841; 5,284,136; 5,376,476; 5,036,849; 5,540,727; 5,836,987;6,044,298; and 6,055,454, which are hereby incorporated herein byreference in their respective entireties. It is understood that ITCSdevice configurations can provide for non-physiologic pacing support inaddition to, or to the exclusion of, bradycardia and/or anti-tachycardiapacing therapies. Exemplary cardiac monitoring circuitry, structures andfunctionality, aspects of which can be incorporated in an ITCS of thepresent invention, are disclosed in commonly owned U.S. Pat. Nos.5,313,953; 5,388,578; and 5,411,031, which are hereby incorporatedherein by reference in their respective entireties.

An ITCS device can incorporate circuitry, structures and functionalityof the subcutaneous implantable medical devices disclosed in commonlyowned U.S. Pat. Nos. 5,203,348; 5,230,337; 5,360,442; 5,366,496;5,397,342; 5,391,200; 5,545,202; 5,603,732; and 5,916,243 and commonlyowned U.S. Patent Applications Ser. No. 60/462,272, filed Apr. 11, 2003,Ser. No. 10/462,001, filed Jun. 13, 2003, Ser. No. 10/465,520, filedJun. 19, 2003, Ser. No. 10/820,642 filed Apr. 8, 2004 and Ser. No.10/821,248, filed Apr. 8, 2004 which are incorporated herein byreference.

The housing of the ITCS device may incorporate components of amonitoring unit 409, including a memory, sensor interface, and/or eventdetector circuitry. The monitoring unit 409 may be coupled to one ormore sensors, patient input devices, and/or information systems asdescribed in connection with FIG. 2. In some embodiments, the housing ofthe ITCS device may also incorporate components of a therapy feedbackunit. In other embodiments, circuitry to implement the therapy feedbackunit may be configured within a separate device from the monitoringunit. In this embodiment, the therapy feedback unit and the monitoringunit may be communicatively coupled using leads or a wirelesscommunication link, for example.

In one implementation, the ITCS device may include an impedance sensorconfigured to sense the patient's transthoracic impedance. The impedancesensor may include the impedance drive/sense circuitry incorporated withthe housing 402 of the ITCS device and coupled to impedance electrodespositioned on the can or at other locations of the ITCS device, such ason the subcutaneous electrode assembly 407 and/or lead assembly 406. Inone configuration, the impedance drive circuitry generates a currentthat flows between a subcutaneous impedance drive electrode and a canelectrode on the primary housing of the ITCS device. The voltage at asubcutaneous impedance sense electrode relative to the can electrodechanges as the patient's transthoracic impedance changes. The voltagesignal developed between the impedance sense electrode and the canelectrode is sensed by the impedance drive/sense circuitry.

Communications circuitry is disposed within the housing 402 forfacilitating communication between the ITCS device, including themonitoring unit 409, and an external communication device, such as aportable or bed-side communication station, patient-carried/worncommunication station, or external programmer, for example. Thecommunications circuitry can also facilitate unidirectional orbidirectional communication with one or more external, cutaneous, orsubcutaneous physiologic or non-physiologic sensors.

FIG. 5 illustrates a block diagram of an external breathing therapydevice 500, e.g., xPAP device that may be used to provide therapy to thepatient for various types of disordered breathing. An implantablemonitoring device, implemented as a component of the CRM or ITCS systemsdescribed in connection with FIGS. 4A and 4B, respectively, may collectinformation related to the breathing therapy.

As previously discussed, the xPAP device 500 may include any of thepositive airway pressure devices, including CPAP, bi-PAP, PPAP, and/orautotitration positive airway pressure devices, for example. Continuouspositive airway pressure (CPAP) devices deliver a set air pressure tothe patient. The pressure level for the individual patient may bedetermined during a titration study. Such a study may take place in asleep lab, and involves determination of the optimum airway pressure bya sleep physician or other professional. The CPAP device pressurecontrol is set to the determined level. When the patient uses the CPAPdevice, a substantially constant airway pressure level is maintained bythe device.

Autotitration PAP devices are similar to CPAP devices, however, thepressure controller for autotitration devices automatically determinesthe air pressure for the patient. Instead of maintaining a constantpressure, the autotitration PAP device evaluates sensor signals and thechanging needs of the patient to deliver a variable positive airwaypressure. Autotitration PAP and CPAP are often used to treat sleepdisordered breathing, for example.

Bi-level positive airway pressure (bi-PAP) devices provide two levels ofpositive airway pressure. A higher pressure is maintained while thepatient inhales. The device switches to a lower pressure duringexpiration. Bi-PAP devices are used to treat a variety of respiratorydysfunctions, including chronic obstructive pulmonary disease (COPD),respiratory insufficiency, and ALS or Lou Gehrig's disease, amongothers.

The xPAP device 500 may be coupled to sensors, input devices, andinformation systems 502, 504, 506 used to sense respiration-relatedand/or other patient conditions. A signal processor 520 may be used tocondition the signals received from the sensors and/or other inputdevices 502, 504, 506. The signal processor 520 may include, forexample, drive circuitry for activating the sensors, as well as filters,amplifiers, and/or A/D conversion circuitry for conditioning the sensorsignals.

The breathing therapy control unit 540 includes a flow generator 542that pulls in air through a filter. The flow generator 542 is controlledby the pressure control circuitry 544 to deliver an appropriate airpressure to the patient. Air flows through tubing 546 coupled to thexPAP device 500 and is delivered to the patient's airway through a mask548. In one example, the mask 548 may be a nasal mask covering only thepatient's nose. In another example, the mask 548 covers the patient'snose and mouth.

The xPAP device 500 may include a communications unit 580 forcommunicating with one or more separate devices, including theimplantable monitoring device, or other remote devices 590. In oneexample, the xPAP device 500 may receive information about the breathingtherapy delivered by the xPAP device 500 from a patient-internal device.In another example, the xPAP device 500 may receive information from ortransmit information to a patient management server or other computingdevice through the communications circuitry 580.

The block diagram of FIG. 6 illustrates an example of medical system 600including a fully or partially implantable device 601 that may be usedto monitor breathing therapy delivered by an external device inaccordance with embodiments of the invention. The system 600 employs amedical device 601 that may be coupled to an array of data acquisitiondevices, including patient-internal sensors 611, patient-externalsensors 612, patient input devices 613, and/or other information systems614 as described herein.

Conditions used to monitor parameters of the breathing therapy mayinclude both physiological and non-physiological contextual conditionsaffecting the patient. Physiological conditions may include a broadcategory of conditions associated with the internal functioning of thepatient's physiological systems, including the cardiovascular,respiratory, nervous, muscle and other systems. Examples ofphysiological conditions include blood chemistry, patient posture,patient activity, respiration quality, sleep quality, among others.

Contextual conditions are non-physiological conditions representingpatient-external or background conditions. Contextual conditions may bebroadly defined to include, for example, present environmentalconditions, such as patient location, ambient temperature, humidity, airpollution index. Contextual conditions may also includehistorical/background conditions relating to the patient, including thepatient's normal sleep time and the patient's medical history, forexample. Methods and systems for detecting some contextual conditions,including, for example, proximity to bed detection, are described incommonly owned U.S. patent application Ser. No. 10/269,611, filed Oct.11, 2002, which is incorporated herein by reference.

Table 1 provides a representative set of patient conditions that may beused to monitor breathing therapy in accordance with embodiments of theinvention. Table 1 also provides illustrative sensing methods that maybe employed to sense the conditions. It will be appreciated that patientconditions and detection methods other than those listed in Table 1 maybe used and are considered to be within the scope of the invention.

TABLE 1 Sensor type or Detection Condition Type Condition methodPhysiological Cardiovascular Heart rate EGM, ECG System Heart ratevariability QT interval Ventricular filling Intracardiac pressurepressure sensor Blood pressure Blood pressure sensor Respiratory SnoringAccelerometer System Microphone Respiration pattern Transthoracic (Tidalvolume Minute impedance sensor (AC) ventilation Respiratory rate)Patency of upper airway Intrathoracic impedance sensor Pulmonarycongestion Transthoracic impedance sensor (DC) Nervous SystemSympathetic nerve Muscle sympathetic activity nerve Activity sensorBrain activity EEG Blood Chemistry CO2 saturation Blood analysis O2saturation Blood alcohol content Adrenalin Brain Natriuretic Peptide(BNP) C-Reactive Protein Drug/Medication/Tobacco use Muscle SystemMuscle atonia EMG Eye movement EOG Patient activity Accelerometer, MV,etc. Limb movements Accelerometer, EMG Jaw movements Accelerometer, EMGPosture Multi-axis accelerometer Contextual/ Environmental Ambienttemperature Thermometer Non- Humidity Hygrometer physiological PollutionAir quality website Time Clock Barometric pressure Barometer Ambientnoise Microphone Ambient light Photodetector Altitude Altimeter LocationGPS, proximity sensor Proximity to bed Proximity to bed sensorHistorical/ Historical sleep time Patient input, previously Backgrounddetected sleep onset times Medical history Patient input Age Recentexercise Weight Gender Body mass index Neck size Emotional statePsychological history Daytime sleepiness Patient perception of sleepquality Drug, alcohol, nicotine use

The implantable device 601 of FIG. 6 includes a monitoring unit 637 thatprocesses signals received from the sensors, 611, 612, patient inputdevices 613, and/or other information system 614. The monitoring unit637 may include one or more a detection units 624, 626, 628 that detectthe occurrence of various physiological events. For example, themonitoring unit 637 may include one or more of a disordered breathingdetector 624, a sleep detector 628, and/or a therapy usage detector 626.Other event detection components may also be included in the monitoringunit 637. The monitoring unit 637 may include circuitry used tocalculate various indices, such as AHI, % PB, arousals per unit time,and/or other indices that can be used to evaluate therapy efficacy,therapy impact and/or other parameters. The monitoring unit 637 maycompare the patient's therapy usage to a prescribed therapy to determinetherapy compliance.

The disordered breathing detector 624 may be coupled to a respirationsensor, for example, and used to detect disordered breathing eventsbased on the inspiratory and expiratory phases of the patient'srespiration cycles, for example. The sleep detector 628 may analyzevarious inputs from the patient-internal sensors 611, patient-externalsensors 612, patient input devices 613, and/or other information systems614 to detect sleep-related events, including, for example, sleep onset,sleep offset, sleep stages, and arousals from sleep.

The therapy usage detector may detect the proximity of the patient tothe external breathing device, to determine therapy usage. In anotherexample, the therapy usage detector may analyze the patient'srespiration waveform to determine therapy usage.

The monitoring unit 637 may operate in cooperation with a memory 636.The memory 636 may store information derived from signals produced bythe patient-internal sensors 611, patient-external sensors 612, patientinput devices 613, and/or other information systems 614. The memory 636may also store information about detected events, e.g., sleep anddisordered breathing events, and/or information related to calculatedindices characterizing various events such as sleep and/or disorderedbreathing events. The stored data, along with other information relatedto the breathing therapy may be transmitted to another component of themedical device 601 or to a separate device 640 for storage, furtherprocessing, trending, analysis, printing and/or display, for example. Inone scenario, the stored data can be downloaded to a separate deviceperiodically or on command. The stored data may be presented to thepatient's health care professional on a real-time basis, or as along-term, e.g., month long or year long, trend of daily measurements.

The medical device 601 may optionally include a therapy unit. In variousexamples provided herein, the medical device 601 is a cardiac deviceconfigured to deliver cardiac electrical stimulation therapy using acardiac pulse generator 675 and electrical stimulation electrodes 652.

The medical device 601 may further include a communications unit 606that controls communications between the medical device 601 and otherdevices or systems. For example, the communications unit 606 may be usedto provide wireless or wired communications links between the medicaldevice 601 and one or more of the patient-internal sensors 611,patient-external sensors 612, patient input devices 613, and informationsystems 614.

The communications unit 606 may also facilitate communications betweenthe medical device 601 and a remote device 640 such as thepatient-external breathing therapy device, a programmer, and/or an APMsystem. The wireless connections coupling the medical device 601 tovarious other devices and systems may utilize a variety of wirelessprotocols, including, for example, Bluetooth, IEEE 802.11, and/or aproprietary wireless protocol.

Detecting the onset, termination, duration, stages, and quality of sleepexperienced by a patient may be employed in connection with monitoringbreathing therapy. Patients suffering from sleep apnea, or other typesof sleep disordered breathing, are generally treated with breathingtherapy only during periods of sleep. Monitoring the sleep disorderedbreathing therapy may involve determining when the patient is asleepand/or monitoring arousals and/or various sleep stages.

In addition, monitoring patient sleep may be used to assess an impact ofbreathing therapy on the patient. Therapy impact information may be usedto determine an appropriate breathing therapy for the patient. Theimplantable monitoring device may include a sleep detector 628 fordetecting when the patient is asleep and the various stages of sleep.Various methods of sleep detection implementable in an implanted deviceinvolve sensing one or more conditions associated with sleep. Thesleep-related conditions may be compared to a threshold to determine ifthe patient is asleep.

The sleep-related conditions may be derived from patient-external orimplantable sensors and analyzed by a sleep detector located in theimplantable monitoring device or by circuitry within the APMcommunication unit (i.e., a supervisor device that co-ordinatesdiagnostics between various sensors. In one implementation proximity tobed, sleep detection may be implemented in an implantable cardiac rhythmmanagement system configured as a pacemaker/defibrillator as illustratedin FIG. 4A or the ITCS device illustrated in FIG. 4B.

Sleep detection may involve sensing one or more conditions indicative ofsleep. A representative set of sleep-related conditions include bodymovement, heart rate, QT interval, eye movement, respiration rate,transthoracic impedance, tidal volume, minute ventilation, body posture,brain activity, cardiac activity, muscle tone, body temperature, time ofday, historical sleep times, blood pressure, and blood gasconcentration, proximity to bed, for example.

Sleep may be detected by comparing levels of the one or moresleep-related conditions to one or more sleep thresholds. For example,sleep may be detected by based on the patient's heart rate. When thepatient's heart rate decreases below a sleep threshold, the patient maybe determined to be asleep. Sleep may also be detected base on thepatient's activity. If the patient's activity decreases below a sleepthreshold, then the patient may be determined to be asleep. Anothermethod of detecting sleep involves monitoring the patient's minuteventilation. If the patient's minute ventilation falls below a sleepthreshold, then the patient may be determined to be asleep.

Sleep may be detected by comparing multiple sleep-related conditions tomultiple thresholds. For example, the patient may be determined to beasleep if the patient's activity, sensed by an accelerometer, fallsbelow an activity sleep threshold and the patient's heart rate, sensedby cardiac electrodes, falls below a heart rate sleep threshold.

Sleep may also be detected using one sleep-related condition to modifythe sleep threshold of another sleep-related condition. A firstsleep-related condition may be sensed. The level of the sleep-relatedcondition may be compared to a sleep threshold to determine the onsetand termination of sleep. A second sleep-related condition may be usedto adjust the sleep threshold. Additional sleep-related conditions mayoptionally be sensed to confirm the onset or termination of the sleepcondition.

A sleep detector 628 (FIG. 6) may be configured to compare the levels ofone or more sleep-related conditions to one or more thresholds. In oneimplementation, the one sleep related condition may be compared to asleep threshold or other index to detect sleep. In anotherimplementation, multiple sleep-related conditions may be compared tomultiple thresholds or indices. In a further implementation, one or moreof the sleep-related conditions may be used to adjust the sleepthresholds or indices. Furthermore, the onset or termination of sleepmay be confirmed using an additional number of sleep-related conditions.

One or more sleep-related conditions may be sensed using implantablesensors and/or patient-external sensors, for example. In one embodiment,patient activity may be compared to a sleep threshold to determine whenthe patient is asleep. A low level of activity is indicative that thepatient is sleeping. Patient activity may be sensed, for example, usingan accelerometer positioned on or in the housing of an implantablecardiac device, or in another convenient location. The accelerometersignal may be correlated with activity level or workload.

A second sleep-related condition may be used to adjust the sleepthreshold. In one embodiment, the patient's minute ventilation is usedto adjust the sleep threshold. The patient's respiration may be sensedusing a transthoracic impedance sensor. Transthoracic impedance may beused to derive various parameters associated with respiration,including, for example, tidal volume and/or minute ventilation. Atransthoracic impedance sensor may be integrated into an implantablecardiac device with intracardiac electrodes, for example. Impedancedriver circuitry generates a current that flows through the bloodbetween the impedance drive electrode and a can electrode on the housingof the cardiac device. The voltage at an impedance sense electroderelative to the can electrode changes as the transthoracic impedancechanges.

The voltage signal developed at the impedance sense electrode,illustrated in FIG. 7, is proportional to the transthoracic impedance,with the impedance increasing during respiratory inspiration anddecreasing during respiratory expiration. The peak-to-peak transition ofthe impedance, illustrated in FIG. 7, is proportional to the amount ofair inhaled in one breath, denoted the tidal volume. The variations inimpedance during respiration may be used to determine the respirationtidal volume, corresponding to the volume of air moved in a breath, orminute ventilation corresponding to the amount of air moved per minute.

FIG. 8 is a flow chart illustrating a method of detecting sleepaccording to an embodiment of the invention. A sleep thresholdassociated with a first sleep-related condition is established. Thesleep threshold may be determined from clinical data of a sleepthreshold associated with sleep acquired using a group of subjects, forexample. The sleep threshold may also be determined using historicaldata taken from the particular patient for whom onset and offset ofsleep is to be determined. For example, a history of a particularpatient's sleep times can be stored, and a sleep threshold can bedeveloped using data associated with the patient's sleep time history.

First and second signals associated with sleep-related conditions aresensed 810, 820. The first and the second signals may be any signalassociated with the condition of sleep, such as the representativesleep-related conditions associated with sleep listed above.

The sleep threshold established for the first signal is adjusted 830using the second signal. For example, if the second signal indicatescondition, e.g., high level of patient activity that is incompatiblewith a sleep state, the sleep threshold of the first signal may beadjusted downward to require sensing a decreased level of the firstsignal before a sleep condition is detected.

If the first signal is consistent with sleep according to the adjustedsleep threshold 840, a sleep condition is detected 850. If the firstsignal is not consistent with sleep using the adjusted sleep threshold,the first and the second signals continue to be sensed 810, 820 and thethreshold adjusted 830 until a condition of sleep is detected 850.

In another embodiment of the invention, illustrated in the flow chart ofFIG. 9, an accelerometer and a minute ventilation sensor are used todevelop the first and second signals associated with sleep. Apreliminary accelerometer signal sleep threshold is determined 910. Forexample, the preliminary sleep threshold may be determined from clinicaldata taken from a group of subjects or historical data taken from thepatient over a period of time.

The activity level of the patient is sensed using an accelerometer 920that may be incorporated into an implantable cardiac pacemaker asdescribed above. Alternatively, the accelerometer may be attachedexternally to the patient. The patient's minute ventilation (MV) signalis determined 925. The MV signal may be acquired, for example, based onthe transthoracic impedance signal as described above using animplantable cardiac device. Other methods of determining the MV signalare also possible and are considered to be within the scope of thisinvention.

In this example, the accelerometer signal represents the sleep detectionsignal that is compared to the sleep threshold. The MV signal is thethreshold adjustment signal used to adjust the sleep threshold. Heartrate is determined 930 in this example to provide a sleep confirmationsignal.

Threshold adjustment may be accomplished by using the patient's MVsignal to moderate the accelerometer sleep threshold. If the patient'sMV signal is low relative to an expected MV level associated with sleep,the accelerometer sleep threshold is increased. Similarly, if thepatient's MV signal level is high relative to an expected MV levelassociated with sleep, the accelerometer sleep threshold is decreased.Thus, when the patient's MV level is high, less activity is required tomake the determination that the patient is sleeping. Conversely when thepatient's MV level is relatively low, a higher activity level may resultin detection of sleep. The use of two sleep-related signals to determinea sleep condition enhances the accuracy of sleep detection over previousmethods using only one sleep-related signal to determine that a patientis sleeping.

Various signal processing techniques may be employed to process the rawsensor signals. For example, a moving average of a plurality of samplesof each sleep-related signal may be calculated and used as thesleep-related signal. Furthermore, the sleep-related signals may befiltered and/or digitized. If the MV signal is high 935 relative to anexpected MV level associated with sleep, the accelerometer sleepthreshold is decreased 940. If the MV signal is low 935 relative to anexpected MV level associated with sleep, the accelerometer sleepthreshold is increased 945.

If the sensed accelerometer signal is less than or equal to the adjustedsleep threshold 950, and if the patient is not currently in a sleepstate 965, then the patient's heart rate is checked 980 to confirm thesleep condition. If the patient's heart rate is compatible with sleep980, then sleep onset is determined 990. If the patient's heart rate isincompatible with sleep, then the patient's sleep-related signalscontinue to be sensed.

If the accelerometer signal is less than or equal to the adjusted sleepthreshold 950 and if the patient is currently in a sleep state 965, thena continuing sleep state is determined and the patient's sleep-relatedsignals continue to be sensed for sleep termination to occur.

If the accelerometer signal is greater than the adjusted sleep threshold950 and the patient is not currently in a sleep state 960, then thepatient's sleep-related signals continue to be sensed until sleep onsetis detected 990. If the accelerometer signal is greater than theadjusted sleep threshold 950 and the patient is currently in a sleepstate 960, then sleep termination is detected 970.

The graphs of FIGS. 10-12 illustrate the adjustment of the accelerometersleep threshold using the MV signal. The relationship between patientactivity and the accelerometer and MV signals is trended over a periodof time to determine relative signal levels associated with a sleepcondition. FIG. 10A illustrates activity as indicated by theaccelerometer signal. The patient's heart rate for the same period isgraphed in FIG. 10B. The accelerometer signal indicates a period ofsleep associated with a relatively low level of activity beginning atslightly before 23:00 and continuing through 6:00. Heart rateappropriately tracks the activity level indicated by the accelerometerindicating a similar period of low heart rate corresponding to sleep.The accelerometer trends are used to establish a threshold for sleepdetection.

FIG. 11 is a graph of baseline trending for an MV signal. Historicaldata of minute ventilation of a patient is graphed over an 8 monthperiod. The MV signal trending data is used to determine the MV signallevel associated with sleep. In this example, a composite MV signalusing the historical data indicates a roughly sinusoidal shape with therelatively low MV levels occurring approximately during the period fromhours 21:00 through 8:00. The low MV levels are associated with periodsof sleep. The MV signal level associated with sleep is used to implementsleep threshold adjustment.

FIG. 12 illustrates adjustment of the accelerometer sleep thresholdusing the MV signal. The initial sleep threshold 1210 is establishedusing the baseline accelerometer signal data acquired as discussedabove. If the patient's MV signal is low relative to an expected MVlevel associated with sleep, the accelerometer sleep threshold isincreased 1220. If the patient's MV signal level is high relative to anexpected MV level associated with sleep, the accelerometer sleepthreshold is decreased 1230. When the patient's MV level is high, lessactivity detected by the accelerometer is required to make thedetermination that the patient is sleeping. However, if the patient's MVlevel is relatively low a higher activity level may result in detectionof sleep. The use of two sleep-related signals to adjust a sleepthreshold for determining a sleep condition enhances the accuracy ofsleep detection over previous methods.

Additional sleep-related signals may be sensed and used to improve thesleep detection mechanism described above. For example, a posture sensormay be used to detect the posture of the patient and used to confirmsleep. If the posture sensor indicates a vertical posture, then theposture sensor signal may be used to override a determination of sleepusing the sleep detection and threshold adjustment signals. Othersignals may also be used in connection with sleep determination orconfirmation, including the representative set of sleep-related signalsassociated with sleep indicated above. Methods and systems related tosleep detection, aspects of which may be utilized in connection with themethodologies of the present invention, are described in commonly ownedU.S. patent application Ser. No. 10/309,771, filed Dec. 4, 2002, whichis incorporated herein by reference.

The above described sleep-detection methods may be used fordiscriminating between periods of sleep and periods of wakefulness.Knowledge of sleep onset, offset, arousal episodes, and/or length ofuninterrupted sleep may be used to adjust patient therapy.

Sleep stage discrimination, including REM and non-REM sleep stages mayadditionally be used in connection with external breathing therapy. Forexample, some patients may experience sleep disordered breathingprimarily during particular sleep stages. The implantable device maymonitor sleep stages and disordered breathing episodes. The breathinginformation may be analyzed in view of the sleep stage information. Theanalysis may be helpful in adapting a breathing therapy for a patient,e.g. delivering breathing therapy during sleep stages that predisposethe patient to disordered breathing episodes. In one implementation,sleep stage may be determined using information from an EEG sensor. Inone implementation, sleep information associated with sleep stagesand/or arousals from sleep may be determined using information from anEEG sensor. Systems and methods for detecting arousals from sleep,aspects of which may be utilized in connection with the presentinvention, are described in commonly owned U.S. patent applicationentitled “Autonomic Arousal Detection System and Method,” identified byAttorney Docket Number GUID. 106 PA, filed on Aug. 17, 2004, which isincorporated herein by reference.

In another implementation, sleep stage information may be obtained usingone or more muscle atonia sensors. Methods and systems for implementingof sleep stage detection using muscle atonia sensors are described incommonly owned U.S. patent application Ser. No. 10/643,006, filed onAug. 18, 2003, which is incorporated herein by reference.

Various aspects of sleep quality, including number and severity ofarousals, sleep disordered breathing episodes, limb movements duringsleep, and cardiac, respiratory, muscle, and nervous system functioningduring sleep may provide important information relevant to the deliveryof breathing therapy. Methods and systems for collecting and assessingsleep quality data are described in commonly owned U.S. patentapplication Ser. No. 10/642,998, filed Aug. 18, 2003, which isincorporated herein by reference.

As previously described, monitoring the effectiveness and/or impactand/or other parameters of breathing therapy may involve detectingdisordered breathing episodes. The respiratory disruptions caused bydisordered breathing can be particularly serious for patientsconcurrently suffering from cardiovascular deficiencies, such ascongestive heart failure. Unfortunately, disordered breathing is oftenundiagnosed. If left untreated, the effects of disordered breathing mayresult in serious health consequences for the patient.

Episodes of disordered breathing are associated with acute and chronicphysiological effects. Acute responses to disordered breathing mayinclude, for example, negative intrathoracic pressure, hypoxia, arousalfrom sleep, and increases in blood pressure and heart rate. Duringobstructive apnea episodes, negative intrathoracic pressure may arisefrom an increased effort to generate airflow. Attempted inspiration inthe presence of an occluded airway results in an abrupt reduction inintrathoracic pressure. The repeated futile inspiratory effortsassociated with obstructive sleep apnea may trigger a series ofsecondary responses, including mechanical, hemodynamic, chemical,neural, and inflammatory responses.

Obstructive sleep apneas may be terminated by arousal from sleep severalseconds after the apneic peak, allowing the resumption of airflow.Coincident with arousal from sleep, surges in sympathetic nerveactivity, blood pressure, and heart rate may occur. The adverse effectsof obstructive apnea are not confined to sleep. Daytime sympatheticnerve activity and systemic blood pressure are increased. There may alsobe a sustained reduction in vagal tone, causing reduction in total heartrate variability during periods of wakefulness.

Central sleep apnea is generally caused by a failure of respiratorycontrol signals from the brain. Central sleep apnea is a component ofCheyne-Stokes respiration (CSR), a respiration pattern primarilyobserved in patients suffering from chronic heart failure (CHF).Cheyne-Stokes respiration is a form of periodic breathing in whichcentral apneas and hypopneas alternate with periods of hyperventilationcausing a waxing-waning pattern of tidal volume. In some CHF patients,obstructive sleep apnea and central sleep apnea may coexist. In thesepatients, there may be a gradual shift from predominantly obstructiveapneas at the beginning of the night to predominantly central apneas atthe end of the night.

Several mechanisms may be involved in central apneas observed inpatients suffering from chronic heart failure. According to onemechanism, increased carbon dioxide sensitivity in CHF patients triggershyperventilation initiating a sleep apnea episode. Breathing isregulated by a negative feedback system that maintains the arterialpartial pressure of carbon dioxide (PaCO₂) within limits. Changes inPaCO₂ lead to changes in ventilation wherein the greater the sensitivityto carbon dioxide, the greater the ventilatory response.

In patients with cardiopulmonary disorders, an increase in carbondioxide sensitivity may minimize disturbances in PaCO₂, thus protectingthem against the long-term consequences of hypercapnia, an excess ofcarbon dioxide in the blood. Although this protective mechanism may bebeneficial while the patient is awake, the increased sensitivity tocarbon dioxide may disrupt breathing during sleep.

During sleep, ventilation decreases and PaCO₂ levels increase. If thePaCO₂ level decreases below level referred to as the apneic threshold,ventilation stops, central sleep apnea begins, and PaCO₂ rises toprevious levels.

In patients with increased sensitivity to carbon dioxide, thenegative-feedback system that controls breathing initiates a largerespiratory drive when PaCO₂ rises. The large respiratory drive produceshyperventilation. Hyperventilation, by driving the PaCO₂ level below theapneic threshold, results in central sleep apnea. As a result of theapnea, the PaCO₂ level rises again, leading to an increase inventilation. In this way, cycles of hyperventilation and central apneamay recur throughout sleep.

The posture of congestive heart failure (CHF) patients during sleep mayalso be implicated in triggering apnea. When CHF patients lie down, theprone posture may create fluid accumulation and pulmonary congestioncausing the patient to reflexively hyperventilate. The hyperventilationmay lead to the cyclical pattern of hyperventilation-apnea describedabove.

Arousals are not necessarily required in central sleep apneas forbreathing to resume at the termination of the apnea event. In centralapnea, the arousals follow the resumption of breathing after an apneaevent. The arousals may facilitate development of oscillations inventilation by stimulating hyperventilation and reducing PaCO₂ below theapneic threshold. Cycles of alternating hyperventilation and apnea aresustained by the combination of increased respiratory drive, pulmonarycongestion, sleep interruptions, and apnea-induced hypoxia causing PaCO₂oscillations above and below the apneic threshold. Shifts in thepatient's state of consciousness, particularly with repeated arousals,may further destabilize breathing.

With the transition from wakefulness to non-rapid eye movement (NREM)sleep, the neural drive to breathe decreases from the waking state, andthe threshold for a respiratory response to carbon dioxide increases.Therefore, if the patient's PaCO₂ level during wakefulness is below thishigher sleeping threshold, the transition to NREM sleep may beaccompanied by a brief loss of respiratory drive triggering a centralapnea. During the apnea, the PaCO₂ rises until it reaches the new higherthreshold level and initiates breathing. If the patient transitions intosleep, regular breathing resumes. However, if an arousal occurs, theincreased PaCO₂ level associated with sleep is too high for a state ofwakefulness and will stimulate hyperventilation. Thus, although arousalsterminate obstructive sleep apneas, arousals may initiate respiratoryoscillations associated with central apneas, in particular,Cheyne-Stokes respiration.

In addition to the acute responses to sleep disordered breathing, suchas those discussed above, sleep disordered breathing is also associatedwith a number of secondary or chronic responses, including, for example,chronic decrease in heart rate variability (HRV) and blood pressurechanges. Patients with central sleep apnea may have higher urinary andcirculating norepinephrine concentrations and lower PaCO₂ during bothsleep and wakefulness.

Disordered breathing may be detected by sensing and analyzing variousconditions associated with disordered breathing. Table 2 providesexamples of how a representative subset of the physiological andcontextual conditions listed in Table 1 may be used in connection withdisordered breathing detection.

Detection of disordered breathing may involve comparing one condition ormultiple conditions to one or more thresholds or other indicesindicative of disordered breathing. A threshold or other indexindicative of disordered breathing may comprise a predetermined level ofa particular condition, e.g., blood oxygen level less than apredetermined amount. A threshold or other index indicative ofdisordered breathing may comprises a change in a level of a particularcondition, e.g., heart rate decreasing from a sleep rate to lower ratewithin a predetermined time interval.

In one approach, the relationships between the conditions may beindicative of disordered breathing. In this embodiment, disorderedbreathing detection may be based on the existence and relative valuesassociated with two or more conditions. For example, if condition A ispresent at a level of x, then condition B must also be present at alevel of f(x) before a disordered breathing detection is made.

The thresholds and/or relationships indicative of disordered breathingmay be highly patient specific. The thresholds and/or relationshipsindicative of disordered breathing may be determined on a case-by-casebasis by monitoring conditions affecting the patient and monitoringdisordered breathing episodes. The analysis may involve determininglevels of the conditions and/or relationships between the conditionsassociated, e.g., statistically correlated, with disordered breathingepisodes. The thresholds and/or relationships used in disorderedbreathing detection may be updated periodically to track changes in thepatient's response to disordered breathing.

TABLE 2 Condition Examples of how condition may be used Type Conditionin disordered breathing detection Physiological Heart rate Decrease inheart rate may indicate disordered breathing episode. Increase in heartrate may indicate autonomic arousal from a disordered breathing episode.Decrease in heart rate may indicate the patient is asleep. Heart ratevariability Disordered breathing causes heart rate variability todecrease. Changes in HRV associated with sleep disordered breathing maybe observed while the patient is awake or asleep QT Interval May be usedto detect sleep apnea. Ventricular filling May be used toidentify/predict pulmonary pressure congestion associated withrespiratory disturbance. Blood pressure Swings in on-line blood pressuremeasures are associated with apnea. Disordered breathing generallyincreases blood pressure variability - these changes may be observedwhile the patient is awake or asleep. Snoring Snoring is associated witha higher incidence of obstructive sleep apnea and may be used to detectdisordered breathing. Snoring indicates that the patient is asleep.Respiration Respiration patterns including, e.g., pattern/raterespiration rate, may be used to detect disordered breathing episodes.Respiration patterns may be used to determine the type of disorderedbreathing. Respiration patterns may be used to detect that the patientis asleep. Patency of upper Patency of upper airway is related to airwayobstructive sleep apnea and may be used to detect episodes ofobstructive sleep apnea. Pulmonary congestion Pulmonary congestion isassociated with respiratory disturbances. Sympathetic nerve End of apneaassociated with a spike in activity SNA. Changes in SNA observed whilethe patient is awake or asleep may be associated with sleep disorderedbreathing. Electroencephalogram May be used to detect sleep. (EEG) Maybe used to determine sleep stages, including REM and non-REM sleepstages. CO2 Low CO2 levels initiate central apnea. May be used topredict central apnea risk. O2 O2 desaturation occurs during severeapnea/hypopnea episodes. May be used to evaluate a presence and severityof sleep disordered breathing events. Blood alcohol content Alcoholtends to increase incidence of snoring & obstructive apnea. AdrenalinEnd of apnea associated with a spike in blood adrenaline. BrainNatruiretic A marker of heart failure status, which is Peptide (BNP)associated with Cheyne-Stokes Respiration C-Reactive Protein A measureof inflammation that may be related to apnea. Drug/Medication/TobaccoThese substances may affect the use incidence of both central &obstructive apnea. Muscle atonia Muscle atonia may be used todiscriminate REM from non-REM sleep. Eye movement Eye movement may beused to discriminate REM from non-REM sleep. Contextual/ TemperatureAmbient temperature may be a condition Non- predisposing the patient toepisodes of Physiological disordered breathing and may be useful indisordered breathing detection. Humidity Humidity may be a conditionpredisposing the patient to episodes of disordered breathing and may beuseful in disordered breathing detection. Pollution Pollution may be acondition predisposing the patient to episodes of disordered breathingand may be useful in disordered breathing detection. Posture Posture maybe used to confirm or determine the patient is asleep. Activity Patientactivity may be used in relation to sleep detection. Location Patientlocation may used to determine if the patient is in bed as a part ofsleep detection. Altitude Lower oxygen concentrations at higheraltitudes tends to cause more central apnea

In various implementations, episodes of disordered breathing may bedetected and classified by analyzing the patient's respiration patterns.Methods and systems of disordered breathing detection based onrespiration patterns are further described in commonly owned U.S. patentapplication Ser. No. 10/309,770, filed Dec. 4, 2002, which isincorporated herein be reference.

FIG. 7 illustrates normal respiration as represented by a signalproduced by a transthoracic impedance sensor. The transthoracicimpedance increases during respiratory inspiration and decreases duringrespiratory expiration. During non-REM sleep, a normal respirationpattern includes regular, rhythmic inspiration—expiration cycles withoutsubstantial interruptions.

In one embodiment, episodes of disordered breathing may be detected byevaluating the respiratory waveform output of the transthoracicimpedance sensor. When the tidal volume (TV) of the patient'srespiration, as indicated by the transthoracic impedance signal, fallsbelow a hypopnea threshold, then a hypopnea event is declared. Forexample, a hypopnea event may be declared if the patient's tidal volumefalls below about 50% of a recent average tidal volume or other baselinetidal volume value. If the patient's tidal volume falls further to anapnea threshold, e.g., about 10% of the recent average tidal volume orother baseline value, an apnea event is declared.

In another embodiment, detection of disordered breathing involvesdefining and examining a number of respiratory cycle intervals. FIG. 13illustrates respiration intervals used for disordered breathingdetection according to embodiments of the invention. A respiration cycleis divided into an inspiration period corresponding to the patientinhaling, an expiration period, corresponding to the patient exhaling,and a non-breathing period occurring between inhaling and exhaling.Respiration intervals are established using inspiration 1310 andexpiration 1320 thresholds. The inspiration threshold 1310 marks thebeginning of an inspiration period 1330 and is determined by thetransthoracic impedance signal rising above the inspiration threshold1310. The inspiration period 1330 ends when the transthoracic impedancesignal is maximum 1340. A maximum transthoracic impedance signal 1340corresponds to both the end of the inspiration interval 1330 and thebeginning of the expiration interval 1350. The expiration interval 1350continues until the transthoracic impedance falls below an expirationthreshold 1320. A non-breathing interval 1360 starts from the end of theexpiration period 1350 and continues until the beginning of the nextinspiration period 1370.

Detection of sleep apnea and severe sleep apnea according to embodimentsof the invention is illustrated in FIG. 14. The patient's respiration issensed and the respiration cycles are defined according to inspiration1430, expiration 1450, and non-breathing 1460 intervals as described inconnection with FIG. 13. A condition of sleep apnea is detected when anon-breathing period 1460 exceeds a first predetermined interval 1490,denoted the sleep apnea interval. A condition of severe sleep apnea isdetected when the non-breathing period 1460 exceeds a secondpredetermined interval 1495, denoted the severe sleep apnea interval.For example, sleep apnea may be detected when the non-breathing intervalexceeds about 10 seconds, and severe sleep apnea may be detected whenthe non-breathing interval exceeds about 20 seconds.

Hypopnea is a condition of disordered breathing characterized byabnormally shallow breathing. FIGS. 15A-15B are graphs of tidal volumederived from transthoracic impedance measurements. The graphs comparethe tidal volume of a normal breathing cycle to the tidal volume of ahypopnea episode. FIG. 15A illustrates normal respiration tidal volumeand rate. As shown in FIG. 15B, hypopnea involves a period of abnormallyshallow respiration.

According to an embodiment of the invention, hypopnea is detected bycomparing a patient's respiratory tidal volume to a hypopnea tidalvolume threshold. The tidal volume for each respiration cycle is derivedfrom transthoracic impedance measurements acquired in the mannerdescribed above. The hypopnea tidal volume threshold may be establishedusing clinical results providing a representative tidal volume andduration of hypopnea events. In one configuration, hypopnea is detectedwhen an average of the patient's respiratory tidal volume taken over aselected time interval falls below the hypopnea tidal volume threshold.Furthermore, various combinations of hypopnea cycles, breath intervals,and non-breathing intervals may be used to detect hypopnea, where thenon-breathing intervals are determined as described above.

FIG. 16 is a flow chart illustrating a method of apnea and/or hypopneadetection according to embodiments of the invention. Various parametersare established 1601 before analyzing the patient's respiration fordisordered breathing episodes, including, for example, inspiration andexpiration thresholds, sleep apnea interval, severe sleep apneainterval, and hypopnea tidal volume threshold.

The patient's transthoracic impedance is measured 1605 as described inmore detail above. If the transthoracic impedance exceeds 1610 theinspiration threshold, the beginning of an inspiration interval isdetected 1615. If the transthoracic impedance remains below 1610 theinspiration threshold, then the impedance signal is checked 1605periodically until inspiration 1615 occurs.

During the inspiration interval, the patient's transthoracic impedanceis monitored until a maximum value of the transthoracic impedance isdetected 1620. Detection of the maximum value signals an end of theinspiration period and a beginning of an expiration period 1635.

The expiration interval is characterized by decreasing transthoracicimpedance. When the transthoracic impedance falls 1640 below theexpiration threshold, a non-breathing interval is detected 1655.

If the transthoracic impedance does not exceed 1660 the inspirationthreshold within a first predetermined interval 1665, denoted the sleepapnea interval, then a condition of sleep apnea is detected 1670. Severesleep apnea is detected 1680 if the non-breathing period extends beyonda second predetermined interval 1675, denoted the severe sleep apneainterval.

When the transthoracic impedance exceeds 1660 the inspiration threshold,the tidal volume from the peak-to-peak transthoracic impedance iscalculated, along with a moving average of past tidal volumes 1685. Thepeak-to-peak transthoracic impedance provides a value proportional tothe tidal volume of the respiration cycle. This value is compared to ahypopnea tidal volume threshold 1690. If the peak-to-peak transthoracicimpedance is consistent with the hypopnea tidal volume threshold 1690for a predetermined time 1692, then a hypopnea cycle is detected 1695.

Additional sensors, such as motion sensors, oximetry sensors, and/orposture sensors, may be used to confirm or verify the detection of asleep apnea or hypopnea episode. The additional sensors may be employedto prevent false or missed detections of sleep apnea/hypopnea due toposture and/or motion related artifacts.

Another embodiment of the invention involves classifying respirationpatterns as disordered breathing episodes based on the breath intervalsand/or tidal volumes of one or more respiration cycles within therespiration patterns. According to this embodiment, the duration andtidal volumes associated with a respiration pattern are compared toduration and tidal volume thresholds. The respiration pattern isdetected as a disordered breathing episode based on the comparison.

According to principles of the invention, a breath interval isestablished for each respiration cycle. A breath interval represents theinterval of time between successive breaths, as illustrated in FIG. 17.A breath interval 1730 may be defined in a variety of ways, for example,as the interval of time between successive maxima 1710, 1720 of theimpedance signal waveform.

Detection of disordered breathing, in accordance with embodiments of theinvention, involves the establishment of a duration threshold and atidal volume threshold. If a breath interval exceeds the durationthreshold, an apnea event is detected. Detection of sleep apnea, inaccordance with this embodiment, is illustrated in the graph of FIG. 17.Apnea represents a period of non-breathing. A breath interval 1730exceeding a duration threshold 1740 comprises an apnea episode.

Hypopnea may be detected using the duration threshold and tidal volumethreshold. A hypopnea event represents a period of shallow breathing.Each respiration cycle in a hypopnea event is characterized by a tidalvolume less than the tidal volume threshold. Further, the hypopnea eventinvolves a period of shallow breathing greater than the durationthreshold.

A hypopnea detection approach, in accordance with embodiments of theinvention, is illustrated in FIG. 18. Shallow breathing is detected whenthe tidal volume of one or more breaths is below a tidal volumethreshold 1810. If the shallow breathing continues for an intervalgreater than a duration threshold 1820, then the breathing patternrepresented by the sequence of shallow respiration cycles, is classifiedas a hypopnea event.

FIGS. 19 and 20 provide charts illustrating classification of individualdisordered breathing events and series of periodically recurringdisordered breathing events, respectively. As illustrated in FIG. 19,individual disordered breathing events may be grouped into apnea,hypopnea, tachypnea and other disordered breathing events. Apnea eventsare characterized by an absence of breathing. Intervals of reducedrespiration are classified as hypopnea events. Tachypnea events includeintervals of rapid respiration characterized by an elevated respirationrate.

As illustrated in FIG. 19, apnea and hypopnea events may be furthersubdivided as either central events, related to central nervous systemdysfunction, or obstructive events, caused by upper airway obstruction.A tachypnea event may be further classified as a hyperpnea event,represented by hyperventilation, i.e., rapid deep breathing. A tachypneaevent may alternatively be classified as rapid breathing, typically ofprolonged duration.

FIG. 20 illustrates classification of combinations of periodicallyrecurring disordered breathing events. Periodic breathing may beclassified as obstructive, central or mixed. Obstructive periodicbreathing is characterized by cyclic respiratory patterns with anobstructive apnea or hypopnea event in each cycle. Central periodicbreathing involves cyclic respiratory patterns including a central apneaor hypopnea event in each cycle. Periodic breathing may also be of mixedorigin. Mixed origin periodic breathing is characterized by cyclicrespiratory patterns having a mixture of obstructive and central apneaevents in each cycle. Cheyne-Stokes is a particular type of periodicbreathing involving a gradual waxing and waning of tidal volume andhaving a central apnea and hyperpnea event in each cycle. Othermanifestations of periodic breathing are also possible. Disorderedbreathing episodes may be classified based on the characteristicrespiration patterns associated with particular types of disorderedbreathing.

As illustrated in FIGS. 21A-E, a respiration pattern detected as adisordered breathing episode may include only an apnea respiration cycle2110 (FIG. 21A), only hypopnea respiration cycles 2150 (FIG. 21D), or amixture of hypopnea and apnea respiration cycles 2120 (FIG. 21B), 2130(FIG. 21C), 2160 (FIG. 21E). A disordered breathing event 2120 may beginwith an apnea respiration cycle and end with one or more hypopneacycles. In another pattern, the disordered breathing event 2130 maybegin with hypopnea cycles and end with an apnea cycle. In yet anotherpattern, a disordered breathing event 2160 may begin and end withhypopnea cycles with an apnea cycle in between the hypopnea cycles.

FIG. 22 is a flow graph of a method for detecting disordered breathingin accordance with embodiments of the invention. The method illustratedin FIG. 22 operates by classifying breathing patterns using breathintervals in conjunction with tidal volume and duration thresholds aspreviously described above. In this example, a duration threshold and atidal volume threshold are established for determining both apnea andhypopnea breath intervals. An apnea episode is detected if the breathinterval exceeds the duration threshold. A hypopnea episode is detectedif the tidal volume of successive breaths remains less than the tidalvolume threshold for a period in excess of the duration threshold. Mixedapnea/hypopnea episodes may also occur. In these cases, the period ofdisordered breathing is characterized by shallow breaths ornon-breathing intervals. During the mixed apnea/hypopnea episodes, thetidal volume of each breath remains less than the tidal volume thresholdfor a period exceeding the duration threshold.

Transthoracic impedance is sensed and used to determine the patient'srespiration cycles. Each breath 2210 may be characterized by a breathinterval, the interval of time between two impedance signal maxima, anda tidal volume (TV).

If a breath interval exceeds 2215 the duration threshold, then therespiration pattern is consistent with an apnea event, and an apneaevent trigger is turned on 2220. If the tidal volume of the breathinterval exceeds 2225 the tidal volume threshold, then the breathingpattern is characterized by two respiration cycles of normal volumeseparated by a non-breathing interval. This pattern represents a purelyapneic disordered breathing event, and apnea is detected 2230. Becausethe final breath of the breath interval was normal, the apnea eventtrigger is turned off 2232, signaling the end of the disorderedbreathing episode. However, if the tidal volume of the breath intervaldoes not exceed 2225 the tidal volume threshold, the disorderedbreathing period is continuing and the next breath is checked 2210.

If the breath interval does not exceed 2215 the duration threshold, thenthe tidal volume of the breath is checked 2235. If the tidal volume doesnot exceed 2235 the tidal volume threshold, the breathing pattern isconsistent with a hypopnea cycle and a hypopnea event trigger is set on2240. If the tidal volume exceeds the tidal volume threshold, then thebreath is normal.

If a period of disordered breathing is in progress, detection of anormal breath signals the end of the disordered breathing. If disorderedbreathing was previously detected 2245, and if the disordered breathingevent duration has not exceeded 2250 the duration threshold, and thecurrent breath is normal, then no disordered breathing event is detected2255. If disordered breathing was previously detected 2245, and if thedisordered breathing event duration has extended for a period of timeexceeding 2250 the duration threshold, and the current breath is normal,then the disordered breathing trigger is turned off 2260. In thissituation, the duration of the disordered breathing episode was ofsufficient duration to be classified as a disordered breathing episode.If an apnea event was previously triggered 2265, then an apnea event isdeclared 2270. If a hypopnea was previously triggered 2265, then ahypopnea event is declared 2275.

As previously discussed in connection with the flowchart of FIG. 1Babove, the breathing therapy may be modified based on the sensedconditions. Adjustment of the external breathing therapy may involveinitiating, terminating or modifying, the external breathing therapy.The external breathing therapy may be modified based on theeffectiveness of the breathing therapy, the patient's compliance withthe therapy, the impact of the external breathing therapy on thepatient, and/or other factors. Once initiated, the system may continueto monitor parameters associated with the breathing therapy and thebreathing therapy may be modified based on periodically updatedassessments of therapy efficacy, patient comfort during therapy, sleepquality during therapy, interactions between therapies, or otherfactors, for example.

A subset of patient conditions, for example, one or more of therepresentative conditions listed in Table 1, may be used in connectionwith determining patient compliance with the breathing therapy. Anothersubset of patient conditions, which may overlap the conditions used fortherapy compliance, may be used in connection with the detection ofdisordered breathing. Another subset may be used to assess therapyeffectiveness. Yet another subset may be used to determine an impact ofthe therapy on the patient.

Acute responses to disordered breathing may be used to detect disorderedbreathing and both acute and chronic responses may be used to assess theefficacy and impact of disordered breathing therapy. Conditions used toassess therapy effectiveness may be different from, or the same as,conditions used to assess an impact of the therapy on the patient. Table3 provides a representative set of conditions that may be used fortherapy assessment with respect to both therapy efficacy and therapyimpact.

TABLE 3 Condition Therapy Impact Therapy Efficacy Arousal-Based SleepMay be used to assess Fragmentation therapy impact during sleep.Measures Restful sleep (Patient May be used to assess reported) therapyimpact during sleep. Discomfort (Patient May be used to assess reported)therapy impact. Pacing algorithm May be used to assess interactiontherapy impact. Remaining useful life of May be used to assess therapydevice therapy impact. Disturbed Breathing- May be used toanalyze/assess Based Measures efficacy of therapy to mitigate disorderedbreathing episodes. Respiration quality May be used to analyze/assess(Patient reported) efficacy of therapy to mitigate disordered breathingepisodes. Heart rate variability Disordered breathing causes (HRV) heartrate variability to decrease. Therapy may be modified based on changesin HRV Blood pressure Disordered breathing causes blood pressureincrease Sympathetic nerve Changes in sympathetic nerve activity (SNA)activity are caused by disordered breathing. Therapy may be adjustedbased on the level of SNA Blood chemistry A number of disorderedbreathing related changes may occur in a patient's blood chemistry,including, e.g., higher norepinephrine levels, and lower PaCO₂

It is understood that the patient conditions that may be used inconnection the medical systems described herein are not limited to therepresentative sets listed in Tables 1-3 or those described herein.Further, although illustrative sensing methods for detecting the patientconditions listed above are provided, it is understood that the patientconditions may be detected using a wide variety of technologies. Theembodiments and features described in herein are not limited to theparticular patient conditions or the particular sensing technologiesprovided.

In accordance with various embodiments of the invention, conditionsrelated to sleep quality, e.g., sleep fragmentation and/or otherarousal-based measures, patient-reported restful sleep, andpatient-reported discomfort during therapy, may be used to assess theimpact of the therapy on the patient. For example, if a patient isreceiving effective disordered breathing therapy and has low sleepfragmentation, reports restful sleep, and reports no discomfort, theadverse effects of the therapy on the patient may be relatively low. Ifsleep fragmentation is relatively high, or if the patient reportsdiscomfort or feeling tired after sleeping, these conditions mayindicate that therapy is causing sleep disturbances and/or otherundesirable effects.

Because disordered breathing generally occurs during sleep, it may beparticularly important to assess sleep quality during disorderedbreathing therapy delivery. It is undesirable to provide therapy thateliminates the disordered breathing but increases sleep fragmentation.In such a situation, the disordered breathing therapy may exacerbate theadverse effects produced by the respiratory disturbances. Thus, it maybe preferable to assess the impact of the therapy on the patient andadjust the therapy to improve sleep quality.

Sleep fragmentation and sleep disruptions may also occur if disorderedbreathing therapy is ineffective and disordered breathing occurs duringsleep. Therefore, a therapy impact assessment based on detected sleepquality and/or patient-reported restful sleep may preferably take intoaccount an assessment of therapy effectiveness.

Evaluation of the impact of disordered breathing therapy on the patientpreferably takes into consideration the impact of disordered breathingtherapy on the overall therapeutic goals for the patient, includingcardiac pacing goals and disordered breathing goals. The disorderedbreathing therapy may involve a variety of therapy regimens implementedto achieve predetermined therapeutic goals. The effectiveness of thetherapy, or the degree to which the therapy meets one or moretherapeutic goals may be assessed by detecting and analyzing episodes ofdisordered breathing that occur during therapy delivery.

For example, a therapeutic goal may involve terminating a disorderedbreathing episode and the disordered breathing therapy may be adapted toachieve this goal. Additionally, or alternatively, a therapeutic goalmay involve terminating a disordered breathing episode and preventingfurther disordered breathing. In this example situation, the therapyregimen may be adapted to provide a first therapy to terminate thedisordered breathing episode and provide a second preventative therapyto reduce or eliminate further disordered breathing episodes. The secondpreventative therapy may be adapted to reduce episodes of disorderedbreathing below a predetermined disordered breathing episode threshold.A disordered breathing episode threshold may be expressed, for example,in terms of an apnea/hypopnea index (AHI) or percent time in periodicbreathing (% PB).

FIGS. 23 and 24 are flow graphs illustrating methods of adapting adisordered breathing therapy according to embodiments of the invention.The flow chart of FIG. 23 illustrates a method of adapting disorderedbreathing therapy to achieve a desired level of therapy efficacy. Inthis embodiment, a first set of conditions associated with disorderedbreathing is detected 2310 and used to determine if a disorderedbreathing episode is occurring. If disordered breathing is detected2320, disordered breathing therapy is delivered 2330 to the patient tomitigate the disordered breathing. In one embodiment, the therapydelivered to the patient may initially involve air delivered at a firstpredetermined pressure.

A second set of conditions associated with therapy effectiveness issensed 2340 and used to assess the effectiveness of the therapy. Thedetected conditions used to assess the efficacy of the therapy and adaptthe therapy to mitigate disordered breathing may represent one or moreof the acute conditions associated with disordered breathing, e.g.,detected episodes of interrupted breathing, hypoxia, arousals, negativeintrathoracic pressure, blood pressure, and heart rate or blood pressuresurges.

Additionally, or alternatively, the conditions used to assess therapyefficacy and adapt the breathing therapy may include one or more chronicconditions associated with disordered breathing, including, for example,decreased heart rate variability, increased blood pressure, chronicchanges in sympathetic nerve activity, and changes in blood chemistry,such as increased levels of PaCO₂ and norepinephrine levels, amongothers.

In general, a therapeutic goal in the treatment of disordered breathingis to provide the least aggressive therapy that effectively mitigates,terminates or prevents the patient's disordered breathing or achieves aparticular therapeutic goal associated with disordered breathingtherapy. The disordered breathing therapy regimen may be enhanced byincreasing the intensity or level of therapy to more effectivelymitigate the disordered breathing. Alternatively, the disorderedbreathing therapy regimen may be enhanced by reducing the intensity orlevel of therapy while maintaining a desired decrease in the severity orfrequency of disordered breathing episodes, thus reducing undesirableside effects from the therapy and extending the device lifetime.

If the therapy effectiveness is acceptable 2350, e.g., terminates orreduces the patient's disordered breathing or meets some other desiredgoal, then the therapy may be adapted 2360 to provide a less aggressivetherapy, e.g., air delivered at a decreased pressure. If the therapy isnot effective 2350, then the therapy may be adapted 2370 to enhancetherapy efficacy by providing a more aggressive therapy, e.g.,delivering air at an increased pressure.

In one embodiment, therapy may be determined to be ineffective ifdisordered breathing continues unmitigated following therapy delivery.In this situation, the therapy may be adapted to provide a moreaggressive therapy. In another embodiment, if the disordered breathingdecreases sufficiently in severity, or is otherwise sufficientlymitigated, the therapy may be enhanced by adapting the therapy toprovide a less aggressive therapy, e.g., decreased air pressure. Aspreviously discussed, a less aggressive therapy is preferable to reducethe risk of arousal and to provide a more comfortable therapy to thepatient, for example.

The flowchart of FIG. 24 illustrates a method of adapting a disorderedbreathing therapy in accordance with embodiments of the invention. Inthis example, a first set of conditions associated with disorderedbreathing is detected 2410 and used to determine if a disorderedbreathing episode is occurring. If disordered breathing is detected2420, therapy is delivered 2430 to the patient to mitigate thedisordered breathing.

A second set of conditions is detected 2440 and used to adapt thetherapy. Based on the second set of sensed conditions, the therapyefficacy is assessed 2445. If the therapy efficacy is not acceptable2450, then the therapy may be adapted 2460 to enhance therapy efficacy.If the therapy efficacy is acceptable 2450, then the impact of thetherapy on the patient may be assessed 2470.

If the therapy impact on the patient is acceptable 2480, the systemcontinues to deliver the therapy. When the therapy regimen is complete2485, then therapy is terminated 2490. If the therapy impact on thepatient exceeds acceptable limits, the therapy impact is not acceptable2480, and the therapy may be adapted 2460 to reduce the therapy impact.

The methods illustrated in the flow graphs of FIGS. 23 and 24contemplate real-time monitoring breathing therapy parameters allowingthe therapy system to dynamically adjust the therapy regimen toaccommodate the changing needs of the patient. In one configuration, thetherapy may be adjusted during the period that therapy is delivered tothe patient. In another configuration, the therapy may be adaptedbetween disordered breathing episodes or from night-to-night based onassessment of the efficacy of therapy delivered in connection with oneor more previously detected disordered breathing episodes.

Methods, devices, and systems implementing a coordinated approach tomonitoring breathing treatment and/or providing therapy for disorderedbreathing may incorporate one or more of the features, structures,methods, or combinations thereof described herein below. For example, amedical system may be implemented to include one or more of the featuresand/or processes described herein. It is intended that such a method,device, or system need not include all of the features and functionsdescribed herein, but may be implemented to include one or more selectedfeatures and functions that provide unique structures and/orfunctionality.

A number of the examples presented herein involve block diagramsillustrating functional blocks used for coordinated monitoring,diagnosis and/or therapy functions in accordance with embodiments of thepresent invention. It will be understood by those skilled in the artthat there exist many possible configurations in which these functionalblocks can be arranged and implemented. The examples depicted hereinprovide examples of possible functional arrangements used to implementthe approaches of the invention.

It is understood that the components and functionality depicted in thefigures and described herein can be implemented in hardware, software,or a combination of hardware and software. It is further understood thatthe components and functionality depicted as separate or discreteblocks/elements in the figures in general can be implemented incombination with other components and functionality, and that thedepiction of such components and functionality in individual or integralform is for purposes of clarity of explanation, and not of limitation.

1. A method of monitoring respiration therapy delivered to a patient,comprising: sensing one or more conditions associated withpatient-external breathing therapy; analyzing a sensed respiratorysignal; and implantably monitoring the patient-external breathingtherapy based on the one or more sensed conditions, wherein implantablymonitoring comprises monitoring the patient's use of thepatient-external breathing therapy based on the respiratory signalanalysis.
 2. The method of claim 1, wherein sensing the one or moreconditions comprises sensing one or more conditions associated withpositive airway pressure breathing therapy.
 3. The method of claim 1,wherein sensing the one or more conditions comprises sensingtransthoracic impedance of the patient.
 4. The method of claim 1,wherein analyzing the sensed respiratory signal comprises analyzing asensed waveform morphology of the sensed respiratory signal.
 5. Themethod of claim 1, wherein analyzing the sensed respiratory signalcomprises detecting a pressure notch indicative of flow controlledbreathing therapy usage in a waveform of the respiratory signal.
 6. Themethod of claim 1, wherein implantably monitoring the patient-externalbreathing therapy comprises implantably monitoring an effectiveness ofthe patient-external breathing therapy.
 7. The method of claim 6,wherein implantably monitoring the effectiveness of the patient-externalbreathing therapy comprises: detecting disordered breathing episodes;and monitoring the effectiveness of the patient-external breathingtherapy based on the detected disordered breathing episodes and thepatient's use of the patient-external breathing therapy.
 8. The methodof claim 1, wherein implantably monitoring the patient's use of thepatient-external breathing therapy comprises comparing the sensedrespiratory signal of the sensed respiratory signal with a respiratorysignal indicating usage of patient-external breathing therapy.
 9. Themethod of claim 1, further comprising comparing a respiratory signalsensed during patient use of the patient-external breathing therapy withsensed respiratory signal during non-use of the patient-externalbreathing therapy to detect signal features that indicate usage of thepatient-external breathing therapy.
 10. The method of claim 9, whereinimplantably monitoring the patient use of the patient-external breathingtherapy comprises comparing the patient use of patient-externalbreathing therapy with a prescribed use of the patient-externalbreathing therapy.
 11. The method of claim 1, further comprisingproviding one or more alert signals associated with the patient use ofthe patient-external breathing therapy.
 12. The method of claim 1,wherein implantably monitoring the patient-external breathing therapycomprises implantably monitoring an impact of the patient-externalbreathing therapy on the patient.
 13. The method of claim 1, whereinimplantably monitoring the patient-external breathing therapy comprisesimplantably monitoring one or more interactions between thepatient-external breathing therapy and another therapy delivered to thepatient.
 14. The method of claim 1, further comprising adapting thepatient-external breathing therapy based on the patient's monitored useof the patient-external breathing therapy.
 15. A medical system,comprising: a sensing system configured to sense one or more conditionsassociated with a patient-external breathing therapy, the one or moreconditions comprising patient proximity to a device delivering thepatient-external breathing therapy; and an implantable monitoringdevice, coupled to the sensing system, the implantable monitoring deviceconfigured to monitor patient use of the patient-external breathingtherapy based on the one or more sensed conditions.
 16. The system ofclaim 15, wherein the patient-external breathing therapy comprisespositive airway pressure therapy.
 17. The system of claim 15, whereinthe implantable monitoring device is disposed within a housing of acardiac therapy device.
 18. The system of claim 15, wherein theimplantable monitoring device is configured to monitor an effectivenessof the patient-external breathing therapy based on the sensedconditions.
 19. The system of claim 15, wherein the implantablemonitoring device comprises a disordered breathing detector configuredto detect disordered breathing using the sensed conditions and tomonitor the patient-external breathing therapy based on the detection ofdisordered breathing.
 20. The system of claim 15, wherein theimplantable monitoring device comprises a communication interface forcommunicatively coupling with a remote device and the implantablemonitoring device is configured to transmit information associated withthe one or more sensed conditions to the remote device.
 21. The systemof claim 15, further comprising a transmitter and receiver distributedbetween the implantable monitoring device and the device delivering thepatient-external breathing therapy, the receiver configured to receive asignal broadcast by the transmitter, reception of the signal indicatingproximity between the implantable monitoring device and the devicedelivering the patient-external breathing therapy.
 22. A medical system,comprising: means for sensing one or more conditions associated withpatient-external breathing therapy; means for analyzing a sensedrespiratory signal; and means for implantably monitoring thepatient-external breathing therapy based on the one or more sensedconditions, wherein implantably monitoring comprises monitoring thepatient's use of the patient-external breathing therapy based on therespiratory signal analysis.
 23. The system of claim 22, whereinanalyzing the sensed respiratory signal comprises analyzing a sensedrespiratory waveform morphology of the sensed respiratory signal. 24.The system of claim 22, wherein analyzing the sensed respiratory signalcomprising detecting a pressure notch in the sensed respiratory signalindicative of flow controlled breathing therapy usage in the respiratorywaveform.
 25. The system of claim 22, further comprising means forcomparing patient usage of the patient-external breathing therapy to aprescribed usage.